 

Analysis of 2000-2008 
Home Health Case-mix 
Change 

July 21, 2010 

 

 

Prepared for 

Centers for Medicare & Medicaid Services 

7500 Security Boulevard 

Baltimore, MD 21244-1850 

 

Prepared by 

Alan White 

Michael Plotzke 

Henry Goldberg 

Carolyn Robinson 

Analysis of 2000-2008 Home Health Case-mix Change
July 21, 2010
Prepared for
Centers for Medicare & Medicaid Services
7500 Security Boulevard
Baltimore, MD 21244-1850
Prepared by
Alan White
Michael Plotzke
Henry Goldberg
Carolyn Robinson
Table

Table of Contents 

1. Overview....................................................................................................................................1 
2. Data............................................................................................................................................1 
2.1. Interim Payment System (IPS) Period Data......................................................................1 
2.2. HH PPS Period Data..........................................................................................................2 
3. Methodology..............................................................................................................................2 
3.1. Models to Examine Relationship Between Patient Characteristics and Case-Mix............4 
3.2. Calculating Real Case-Mix Change..................................................................................9 
4. Results......................................................................................................................................10 
4.1. Changes in Patient Characteristics..................................................................................10 
4.2. Statistical Performance of Regression Models................................................................12 
4.3. Regression Coefficients...................................................................................................12 
4.4. Analysis of Case-Mix Change.........................................................................................14 
IPS Period-2007 Case-Mix Change.................................................................................14 
2007-2008 Case-Mix Change..........................................................................................15 
4.5. Drivers of Real Case-Mix Change...................................................................................17 
5. Discussion.................................................................................................................................23 
Appendix Table 1: Regression Coefficients and Mean Values Used for Calculation of Real 
and Nominal Case-Mix Changes: 2000-2008............................................................................24 
 

1. Overview 




In October 2000, the Centers for Medicare & Medicaid Services (CMS) implemented a prospective 
payment system for home health services provided to fee-for-service Medicare beneficiaries. Under 
the Home Health Prospective payment System (HH PPS), Medicare payment for each 60-day episode 
of care is made based on wage levels in the patients locale and on the episodes classification into a 
home health resource group (HHRG). In January 2008, the 80-group HHRG system was replaced 
by a 153-group system.1 Refinement of the HHRG system was based on a four-equation model that 
accounted for the higher average costs associated with later episodes of care (third or higher) relative 
to early episodes of care. In both the 80- and 153-group HHRG models, patient classification is based 
on the patients characteristics at the start of the episode, as well as the patients use of rehabilitation 
therapy services (physical therapy, occupational therapy, or speech language pathology) during the 
episode. Each HHRG has an associated case-mix weight, which determines how much the payment 
for the specific episode is adjusted from the standardized base payment established for the current 
payment year. 

 

Since implementation of the prospective payment system, there has been a steady increase in the 
average case-mix weight of Medicare home health patients. From 2000  2008, overall observed 
case-mix increased by 19.40%. 

 

Given that case-mix assignment is based on patient assessments completed by home health agencies, 
there are questions about the extent to which these increases reflect real case-mix change that is 
associated with true changes in patient characteristics versus nominal case-mix changes attributable to 
changes in coding practices that lead to case-mix creep. Measuring the proportion of total case-mix 
change that is due to nominal versus real factors has important implications for establishing home 
health payment rates that are accurate and reasonable. 

 

In this paper, we examine the changes in case-mix that occurred by 2008, updating analyses for 2006-
2007 that were described in an earlier report.2 

 

2. Data 


2.1. Interim Payment System (IPS) Period Data 




The IPS period data were used as our baseline period for predicting the relationship between 
covariates and case-mix. These data are from Federal Fiscal Year (FFY) 2000 (October 1, 1999 to 
September 30, 2000), a period when the Home Health Interim Payment System (IPS) was in effect. 
Since home health services were not yet paid on the per-episode basis used under HH PPS, we used 

1 We expanded the case-mix variables included in the payment model by providing additional variables 
including scores for certain wound and skin conditions; and more diagnosis groups such as pulmonary, cardiac, 
and cancer diagnoses. Additional refinements were made to replace the previous single therapy visit threshold 
of 10 to three therapy thresholds (6, 14, and 20 visits) 

2 http://www.cms.gov/HomeHealthPPS/Downloads/Home_Health_Case_Mix_Changes_2006-07.pdf 


Medicare home health claims to construct an analysis file of simulated 60-day episodes, applying 
rules based on the anticipated design of the impending prospective payment system. 

 

To assign case-mix weights to the simulated episodes, we needed the appropriate patient 
characteristic variables. These data were available from the Outcomes and Assessment Information 
Set (OASIS) assessment data collected on all Medicare and Medicaid home health patients, but the 
appropriate assessments needed to be matched to the patients simulated payment episode. While the 
collection of OASIS on all Medicare home health patients began in July 1999, the data collection time 
points for each patient did not always match the starting points of our simulated payment episodes. 
This is because, at that time, OASIS assessments were conducted solely for outcomes monitoring 
purposes. When matching OASIS assessments to simulated payment episodes, we accepted any 
assessment within 14 days of the episode start date. If there were multiple qualifying assessments, we 
chose the closest start/resumption of care assessment for initial episodes, and the closest 
start/resumption or follow-up/recertification assessments for subsequent episodes. In approximately 
18% of cases, no suitable OASIS assessment (close enough to a simulated payment episode start date) 
was available, and those episodes had to be excluded from the analysis. 

 

Episodes with fewer than five visits were also excluded from the analysis because they would be 
considered low utilization payment adjustment (LUPA) episodes under PPS, and would not be paid 
using home health resource groups (HHRGs) in any case. The analysis file for the base period 
included episodes for a 10% sample of beneficiaries that represented 313,447 episodes. For episodes 
with OASIS assessments, an HHRG was assigned using the OASIS information, even though the 
actual claims for the services in the episodes were not paid (in 1999) using HHRGs. 

 

2.2. HH PPS Period Data 




The HH PPS period data consisted of analogous files from Calendar Years 2007 and 2008. These 
data were drawn from the Home Health Datalink file. This database includes 100% of Medicare fee-
for-service home health episode claims from the start of HH PPS linked to matched OASIS 
assessments, data on other Medicare service use by the beneficiary, and additional data on provider 
and beneficiary characteristics. We used data for a 20% sample of Medicare home health users, 
selected based on beneficiary Medicare (HIC) number digits. This analysis file contained 974,974 
episodes for 2007 and 872,518 episodes for 2008. Since these were records from the PPS period, the 
actual paid HHRGs were available (based on the 80 HHRG payment model for 2007 and the 153 
HHRG model (HHRG153) for 2008). In addition, we used the grouper program originally used in 
developing the 153 groups and their weights to assign the 2007 episodes to payment groups for the 
HHRG 153 model. In preparing the files, we corrected the HHRG and its associated case-mix 
relative weight in situations where claims-based information on number of allowed therapy visits 
during the episode was inconsistent with the submitted HHRG on the claim. 

 

 

3. Methodology 




The methodology used to measure case-mix change differs somewhat from the one used in the 
previous report that examined 2006-2007 home health case-mix change. We have changed our 


methodology to account for the increase in the number of HHRGs (from 80 to 153) between 2007 and 
2008. Specifically, we used a two-equation approach to analyze case-mix changes over time: 

 

. Using the 80 HHRG model and data from the IPS period, we estimated a regression-based, 
predictive model of individual case-mix scores (relative weights) based on measures of 
patients demographic characteristics, clinical status, inpatient history, and Medicare costs in 
the time period leading up to their home health episodes. The regression coefficients from 
the IPS period model were applied to episodes from 2007 (classified using the 80 HHRG 
model), allowing one to estimate how much of the change in observed case-mix is 
attributable to changes in patient characteristics between the IPS period and 2007. 




 

. Using the 153 HHRG model and data from 2008, we estimated a model similar to the IPS 
period. The coefficients from this model were applied to episodes from 2007 (using the 153 
HHRG model), allowing estimation of how much of the 2007-2008 change in HHRG153 
case-mix is associated with changes in patient characteristics between 2007 and 2008. 




 

We classify the sources of case-mix change into two major types: real (predicted) and nominal 
(unpredicted). 

 

. Real (predicted) change: This is change that is based on the relationship between patient 
characteristics included in the regression model and case-mix (i.e., coefficients from the 
regression model) and changes in the characteristics of patients over time (i.e., the change in 
mean values of the model predictor variables). Real case-mix change arises from variation in 
the underlying health status of patients, which is represented by predictor variables in the 
model. 




 

. Nominal (unpredicted) change: This is the portion of case-mix change that cannot be 
explained by changes in patient characteristics included in the regression model. Nominal 
case-mix change is assumed to reflect differences over time in agency coding practices 




 

Using the results from both models, we calculate predicted case-mix for 2007 and use those results to 
calculate real and nominal changes in case-mix between the IPS period and 2008. The specific steps 
we take are described below: 

 

. Calculate predicted case-mix for 2007 (80 HHRGs): Using coefficients from the HHRG80 
IPS period model and predictor-variable means from 2007, we calculate predicted case-mix 
for 2007. This is calculated as the sum across all model covariates of the regression 
coefficients multiplied times the mean value of the covariate for 2007. 




 

. Calculate predicted case-mix change for 2007 (153 HHRGs): Using coefficients from the 
HHRG153 2008 model, we calculate predicted HHRG153 case-mix for 2007 based on the 
regression coefficients and the 2007 mean values. 

 



. Calculate real case-mix change for 2000-2007: This is calculated as the difference between 
actual case-mix for the IPS period and predicted case-mix in 2007 using the 80-HHRG 
system. 




 


. Calculate real case-mix change for 2007-2008: This is calculated as the difference between 
actual case-mix for 2008 and predicted case-mix in 2007 using the 153-HHRG system. 




 

. Calculate real case-mix for 2008: This is calculated by multiplying the ratio of actual 2008 
(153-HHRG) case-mix to predicted 2007 153-HHRG case-mix by the predicted case-mix in 
2007 using the 80-HHRG model ((1.3085/1.3060)*(1.1152) = 1.1173). This process 
incorporates the latest grouping system (153-HHRG) into the real case mix measurement 
strategy. 

 



. Calculate percentage of real case-mix change for 2000-2008: We calculate the percent of 
total case-mix change from IPS to 2008 estimated as real by taking the ratio of the predicted 
difference in real case-mix from IPS to 2008 over the difference in actual case-mix from IPS 
to 2008. We refer to this as Ratio 1. 




 

. Calculate percentage of total case-mix change for 2000-2008: We calculate the actual case-
mix percentage increase for 2000-2008 by taking the ratio of 2008 average case-mix over the 
IPS average case-mix. We refer to this as Ratio 2. 




 

. Estimate amount of nominal case-mix change: Finally, we produce the estimate of the 
nominal case-mix percentage increase from IPS to 2008 by multiplying (Ratio 1 minus one) 
by (one minus Ratio 2). 




 

The analyses described in this paper incorporate refinements to the data files, sample creation, and 
variable construction that were discussed in the previous report examining the analysis of 2006-2007 
home health case-mix change. Imputation for living arrangement variables in 2007 was conducted 
using the same methodology as explained in the earlier report. 

 

3.1. Models to Examine Relationship Between Patient 
Characteristics and Case-Mix 




Using data from the baseline (IPS) period and 2008, we estimated two regression models of the 
following basic functional form: 

 

 Relative Payment Weighti = a + *Personal Characteristicsi + ei 

 

where: 

 

Relative Payment Weight for individual i is the relative payment weight for that individuals 
60-day home health episode (based on the then-current 80 HHRGs for the IPS model and the 
153 HHRGs for the 2008 model); 

a is a constant term (to be estimated); 

 is a vector of coefficients (to be estimated); 

Personal Characteristics is the vector of demographic and clinical variables for each 
individual; and 


e is an error term. 

 

Our goal in estimating the models was to predict the case-mix weights, using variables that could be 
created using the available administrative data. As a result, we were not particularly concerned about 
redundancy among variables, as long as groups of variables make sense broadly as correlates of case-
mix. Our interest was in achieving as much predictive power as possible from the variables taken 
together. 

 

The models used in this paper have similar specifications to those in the previous report examining 
2006-2007 home health case-mix change. Compared to those earlier models, more APR DRG groups 
are now available for classifying acute stays and certain measures of patient living arrangements are 
now excluded as discussed below. We review each type of variable included in the models. 

 

. Demographic variables: The demographic variables were included to control for any 
differences in case-mix determination associated with age, gender, and race/ethnicity. The 
following demographic variables were included: 


. Age (age groups 65 to 74, 75 to 84, 85 to 84, and 95 and above; age under 65 is the 
reference category); 


. Gender (male); 


. Race (White and African American; other, including Asian, Hawaiian/Pacific 
Islander, and Native American/Alaskan Native, is the reference category). 




 
In addition, the age variables were interacted with the gender and race dummy variables 
to fully exploit the potential differences of the effect on case-mix from the various 
demographic subgroups. There were a total of 19 demographic variables in the models. 


. Measures of prior utilization: Prior hospital, inpatient rehabilitation, and SNF stays and 
days of care are likely to be associated with home health case-mix for a variety of reasons. 
For example, individuals with a recent rehabilitation facility stay may be recovering from an 
injury or fall and may require substantial amounts of care and further rehabilitation services 
as they continue to recover during their home health episodes. The models included 
measures of utilization of acute care hospital, long-term care hospital, inpatient rehabilitation 
facility, and Medicare skilled nursing facility in the period preceding the home health 
episode: 


o Acute-Care Hospital Days in Period 14 Days Preceding Home Health Episode 


o Acute-Care Hospital Days in Period 15 to 120 Days Preceding Home Health Episode 


o Long-Term-Care Hospital Days in Period 14 Days Preceding Home Health Episode 


o Long-Term-Care Hospital Days in Period 15 to 120 Days Preceding Home Health 
Episode 


o Rehabilitation Facility Days in Period 14 Days Preceding Home Health Episode 


o Rehabilitation Facility Days in Period 15 to 120 Days Preceding Home Health 
Episode 


o Medicare Skilled Nursing Facility Days in Period 14 Days Preceding Home Health 
Episode 


o Medicare Skilled Nursing Facility Days in Period 15 to 120 Days Preceding Home 
Health Episode 






 


3 The APR DRG system was developed in 1990 to address both the severity of illness and risk of mortality over 
all patient populations. The APR DRG system includes four severity of illness classes (minor, moderate, major 
or extreme loss of function) and risk of mortality subclass for each base diagnostic group (minor, moderate, 
major, and extreme). 

. Measures of patient living arrangements: Individuals who live with other people, especially 
spouses and close family members, may have lower home health care needs from third parties 
(home health agencies), resulting in lower home health resource use and lower case-mix, all 
else equal. For the IPS period, the model includes dummy variables indicating the patients 
living status at home: 


o Patient Lives Alone 


o Patient Lives with Other (Not Family, Friends, Paid Help or Spouse) 


o Patient Lives with Other Family 


o Patient Lives with Paid Help 


o Patient Lives with Spouse 






 

These living status variables were the only variables in the models that came from agency-
reported OASIS data. 

 

We did not include these variables in the 2008 model because a large number of episodes were 
missing values for these variables in the OASIS assessment. (This is because these variables 
were dropped from the OASIS follow-up/recertification assessment as of 2003.) The approach 
for imputation discussed in the previous report that examined the analysis of 2006-2007 home 
health case-mix change would not work in this situation because that imputation produced an 
overall mean for all episodes. In order to include these variables in the 2008 model, we need 
values of the living arrangement variables for each individual episode rather than an overall 
mean. Therefore we drop these variables from the model when estimating the 2008 model and 
when predicting case-mix in 2007 using the results from the 2008 model. Note that the mean 
values of the patient living arrangement variables (for episodes where it was available) changed 
little between 2007 and 2008, so the impact of dropping these variables from the 2008 model is 
minimal. Based on the IPS period regression coefficients and the change in mean for these 
variables between 2007-2008, the patient living arrangement variables would have been 
associated with a 0.0009 (0.07%) decrease in real case-mix between 2007-2008 had they been 
included in the model. 

 

. Measures of patients acute care hospital inpatient history: We examined the patients 
acute care hospital inpatient history for the four years preceding the home health episode, 
considering the All Patient Refined Diagnosis Related Group (APR DRG) for the patient 
during his or her most recent inpatient stay3. Approximately 86-89% of beneficiaries with 
home health care episodes in the sample had a hospital stay during the look-back period. 
APR DRGs are designed to predict patient acuity and care needs in acute care hospital 
settings. To the extent that such acute care acuity and needs reflect the patients need for 
more-intensive care in other settings (in this case, in home health settings), APR DRGs are 
reasonable proxy variables for home health resources need (i.e., home health case-mix). The 
models included dummy variables for the following: 





4 The 25-episode cut off was chosen to minimize the estimation of model coefficients with very few 
observations which might result in imprecise estimates. 

5 We provide two examples to demonstrate the process. In the first example, for a particular APR DRG, 
severity level 1 has 50 episodes, severity level 2 has 75 episodes, severity level 3 has 43 episodes, and severity 
level 4 has 30 episodes. For that APR DRG, we include in the model severity levels 1, 2, and 3. In the second 
example, for a particular APR DRG, severity level 1 has 120 episodes, severity level 2 has 0, severity level 3 
has 20, and severity level 4 has 160. For that APR DRG we include in the model severity levels 1 and 4. 

 


o The All Patient Refined Diagnosis Related Group (APR DRG) for the patient during 
his or her most recent inpatient stay. 


o Whether that APR DRG was procedure-based or medically-based. 


o The patients expected risk of mortality at the time of the hospitalization (four levels 
 the reference group is patients with no APR DRGs their relative mortality risk 
cannot be coded). 


o Interactions between the APR DRG and APR DRG severity level 




Based on a patients personal characteristics and comorbidities at the time of the hospital 
stay, each patient within each APR DRG is assigned to one of four severity levels in the APR 
DRG algorithm. The severity levels are specified in the models as interactions, because the 
APR DRG severity levels are developed individually for each APR DRG classification. 
Another reason for setting up the severity level effects as interactions in the 
regression is that this approach allows for interpreting the severity level effects 
relative to a severity level that serves as a reference group for each APR-DRG. 
In cases where the four possible severity levels each met our sample size requirements, the 
reference group (labeled any in Appendix Table 1) is the highest severity level (i.e., 
extreme loss of function); then, to see the effect size of a given severity level, one adds the 
severity level interaction coefficient to the reference group coefficient. In other cases, the 
reference group will be an average effect of the severity levels whose indicator variables are 
left out of the model (note that there may be no sample observations for some severity 
levels). The procedure we used is described operationally in the bullet-points below. 

 

For this year's analyses, we utilized a fuller version of the 3M APR DRG grouper that 
allowed us to expand the number of APR DRG-related variables in the model compared to 
previous years. This allowed us to include more diagnosis groups such as pulmonary, 
cardiac and cancer diagnoses. 

 

We included all APR DRG variables and also the severity interactions in the model if there 
were at least 25 episodes4 in the IPS period that were classified with that APR DRG/severity 
level. For each APR DRG the following steps were taken to determine which APR 
DRG/Severity interactions to include in the model5: 




 

. Identify all severity interactions that have greater than 0 episodes 
(maximum of 4 per APR DRG) 

 



. Identify all severity interactions that have at least 25 episodes 
(maximum of 4 per APR DRG) 

 






. If the number of interactions with at least 25 episodes is smaller than 
the number of interactions with greater than 0 episodes, drop all 
interactions (from step 1) with fewer than 25 episodes. Then, 
include in the model all other interactions identified in the first 
bullet. 

 



. If the number of interactions with at least 25 episodes is equal to the 
number of interactions with greater than 0 episodes, drop the 
interaction (from step 1) representing the highest severity level. 
Then, include in the model all other interactions identified in the first 
bullet. 




 

For the analysis of 2006-2007 home health case-mix change, we consulted with clinical 
experts to review the findings for APR DRGs that had large changes in prevalence over time, 
soliciting input on whether there were external explanations for such changes (e.g. changes 
in coding guidelines) or whether the changes likely reflected actual changes in patient 
conditions. Based on this review, we combined APR DRGS 045 (CVA and precerebral 
occlusion with infarction) and 046 (non-specific (CVA and precerebral occlusion without 
infarction) The judgment of our clinical experts was that changes in coding directions 
suggested that some of the cases that would have been classified in APR DRG 045 in the 
base period would be classified in APR DRG 046 in the follow-up period, creating large 
changes in the frequency of each one that were not related to changes in patient condition. 
Therefore, it was decided to merge them for the analysis. Another decision was to drop APR 
DRG 468 (other kidney and urinary tract diagnoses, signs, and symptoms) from our models. 
This is because it appeared that changes in coding guidance, as well as changes (or lack of 
changes) in specification of the APR DRG in the grouper software produced large changes in 
frequency that appeared to be artifacts rather than related to actual changes in patient 
conditions. Since these issues could not be disentangled with a simple transformation (as 
with the CVA cases), this APR DRG was dropped from the analysis. 

 

The models included a total of 848 APR DRG variables and interactions. Episodes with 
stays classified under an APR DRG that did not meet the sample size requirements are 
included in the models but not represented by an APR DRG variable. However, those 
episodes do have values for the variables representing the procedure- or medically- based 
classification and mortality risk variables. For the IPS period, 60.9% of episodes were 
classified as having had a medical APR DRG while 27.1% were classified as having had a 

procedure based APR DRG. The remainder of the sample did not have an acute 
hospitalization and thus no APR DRG information was available. For 2008, 59.6% of the 
sample was assigned a medically based APR DRG and 26.5% was assigned a procedure 
based APR DRG. 

 

. Measures of home health agency ownership type: The models included dummy variables 
based on the agency's ownership type/type of control, as classified in CMS Provider of 
Service (POS) file: 


o Free-standing, voluntary or non-profit 


o Free-standing, proprietary 


o Free-standing, government-owned 


o Facility-based, voluntary or non-profit 


o Facility-based, proprietary 







6 The Medicare payment increases in each setting in each year were multiplied together, and then an annual 
average increase was calculated. The resulting average annual increases were then raised to the power of 
the average difference in years for episodes in the data files. 

o Facility-based, government-owned 


o Other, voluntary or non-profit 


o Other, proprietary 


o Other, government-owned 






 

The reference category to which the aforementioned dummy variables are compared to is 
unknown agency ownership/control. 

 

. Measures of Medicare Part A payments. After controlling for prior utilization, measures of 
Medicare Part A payments may proxy for the intensity of services in the period preceding the 
home health episode. The models included measures of Medicare Part A payments in the 120 
days preceding the home health episode, by service type: 


o Acute-care hospital payments in 120 days preceding home health episode 


o Long-term-care hospital payments in 120 days preceding home health episode 


o Rehabilitation facility payments in 120 days preceding home health episode 


o Medicare SNF payments in 120 days preceding home health episode 






 

Medicare payments between the IPS period and 2008 periods vary partially due to the 
increases in Medicare payment rates made between the IPS period and 2008 during that time. 
Since we estimate predicted case-mix in 2007 using both the IPS model and the 2008 model, 
we make two sets of adjustments to account for the payment rate changes. When computing 
the 2007 predicted case-mix using the IPS model, we inflated the IPS Medicare payment 
amounts using an inflation factor that was based on the aggregate effect of payment rate 
updates from IPS to 2007.6 We took a similar approach and deflated the 2008 Medicare 
payment amounts to 2007 levels when computing the 2007 predicted case-mix using the 2008 
model. To adjust payments, we divided the payments by the following constants. 

 

 IPS to 2007 2008 to 2007 

. Acute care hospital: 1.252705187 0.96700 


. Long-term care hospital: 1.194385134 0.99148 


. Rehabilitation facility: 1.252727250 0.98400 


. SNF: 1.284680344 0.96775 




 

3.2. Calculating Real Case-Mix Change 




After estimating the models, the results (coefficient estimates) were applied to data from 2007. That 
is, a predicted relative payment weight for each episode in 2007 was estimated with the IPS model 
and also the 2008 model. The methodology outlined in Section 3 was used and the following 
calculations were made: 

 

. Total change in case-mix: We calculate the total difference in case-mix between the IPS 
period and 2008. This was based on the change in average case-mix between the two 
periods. 





. Real (predicted) change in case-mix and percentage of total change in case-mix that is 
real (predicted): Changes over time in patient characteristics and other variables 
included in the model can lead to predicted case-mix changes. We used the regression 
coefficients from the models and values for the variables from 2007 to calculate the 
predicted case-mix for 2007. The differences between the case-mix in the IPS period or 
the case-mix in 2008 and the predicted case-mix in 2007 indicate how much of the case-
mix change is accounted for by observable differences (changes in the independent 
variables) in each model. We divided the predicted change in case-mix by the total 
change in case-mix to calculate the percentage of the total change in case-mix that was 
predicted by the models. 


. Nominal (unpredicted) change in case-mix and percentage of total change in case-mix 
that is nominal (unpredicted): The unpredicted change in case-mix is calculated as the 
difference between the total and predicted change in case-mix. It is a measure of the 
change in case-mix that is not due to observable changes in patient characteristics or 
other variables included in the models. The estimates of the unpredicted change in case-
mix are attributed to changes in agency coding practices. 




 

While there may be observable or unobservable factors related to patient case-mix that were not 
included in the model, it is important to note that the omission of these variables affects estimates of 
case-mix change only if there were changes in the prevalence of these variables between the IPS and 
later periods. Variables that remain constant over time do not contribute to real case-mix change 
regardless of how important they are in predicting case-mix level. 

 

4. Results 




The table in the Appendix presents the results from the IPS and 2008 regression models. It also 
reports means from the IPS period, 2007, and 2008 and measures of the real (expected) case-mix 
change associated with each variable in the model. The real case-mix change associated with a 
variable equals the regression coefficient times the change in mean values relative to the period of 
data used to estimate the model. A positive value means that the change in means that has occurred 
since the IPS period is associated with an expected increase in case-mix; a negative value means that 
the change in means is associated with an expected decrease in case-mix. 

 

4.1. Changes in Patient Characteristics 




We analyzed the means of all of the variables included in the regression models for the IPS period, 
2007, and 2008 (see the Appendix). These changes may indicate differences in patient acuity and real 
case-mix change. Some notable differences in patient characteristics occurred between the two 
periods. 

 

. After adjusting for payment rate updates, there was a decrease in mean acute care hospital 
expenditures in the 120 days preceding the home health episode. This declined from $7,569 
in the IPS period to $6,160 in 2007, a decrease of more than 18%. 




 


7 About 84% of proprietary agencies are classified in the POS file as type Other  they are understood to 
be freestanding About 2% of proprietary agencies are identified as facility based (including hospital-based, 
SNF-based, and rehab-based), the others fall in categories also taken to be freestanding. 

. Average acute care hospital days in the 14 days preceding the home health episode decreased 
from 2.26 in the IPS period, to 1.56 in 2007 and 1.44 in 2008. The average number of 
hospital days in the 15-120 days preceding the home health episode decreased from 4.07 in 
the IPS period to 3.29 in 2007 and 3.16 in 2008. 




 

. The average number of SNF days in the 15-120 days preceding the home health episode 
increased from 2.77 in the IPS period to 3.75 in 2007 and 3.83 in 2008. Mean SNF days in 
the 14 days preceding the episode increased, but not as much, with a mean value of 1.17 days 
in the base period, 1.24 days for 2007 and 1.23 days for 2008. 




 

. There were changes in the distribution of episodes by agency types: 


o The proportion of episodes for other proprietary home health agencies increased from 
29.3% in the IPS period to 54% of episodes in 2007 and 57.2% in 2008. There was 
also a large increase in the proportion of episodes for free-standing proprietary 
agencies, which increased from 4.06% in the IPS period to 7.3% in 2007 and 7.8% in 
2008.7 


o The percentage of episodes for facility-based non-profit agencies decreased from 
29.9 in the IPS period to 13.6% in 2007 and 11.7% in 2008. 


o The proportion of episodes for freestanding government agencies decreased from 
3.9% in the IPS period to 1.9% in 2007 and 1.6% in 2008. 




 
. While the means of most of the APR DRG variables were low, there were large changes in 
the mean values of some APR DRG variables: 


o The prevalence of renal failure was more than twice as high in 2008 (1.68%) than it 
was for the IPS period (0.67%). 


o The proportion of patients who had cardiac defibrillator and heart assist implant was 
more than twice as high in 2008 (0.33%) than in the IPS period (0.13%). 


o The prevalence of coronary artery bypass without cardiac catheterization or 
percutaneous cardiac procedure was only about half as high in 2008 (0.39%) than in 
the IPS period (0.69%). The proportion of this APR DRG with minor severity 
decreased from 0.074% to 0.021%. 


o The prevalence of knee joint replacement increased from 2.76% in the baseline 
period to 3.82% in 2007 and 3.80% in 2008. 


o The prevalence of knee replacement with major severity doubled between the IPS 
period and 2008, increasing from 0.14% to 0.28%. 


o The prevalence of intervertebral disc excision and decompression with major severity 
increased from 0.047% in the IPS period to 0.33% in 2008. 


o For all except the major severity level, the prevalence of heart failure decreased from 
the IPS period to 2008. The overall prevalence decreased from 6.07% in the IPS 
period to 4.57% in 2008. 


o The prevalence of malfunction, reaction, complication of cardiac/vascular device or 
procedure with extreme severity more than doubled between 2000 and 2008, 
increasing from 0.019% to 0.065%. 







o The prevalence of nervous system malignancy decreased by almost half between the 
IPS period and 2008, decreasing from 0.09% to 0.05%. 


o The prevalence of dorsal and lumbar fusion procedures for curvature of the back 
more than doubled, from 0.008% to 0.028%. 






 

4.2. Statistical Performance of Regression Models 




We measured the statistical performance of the regression models using the adjusted R-squared 
statistic, a measure of the percentage of the variation in relative payment weight that is explained or 
predicted by variation in independent variables in the model, adjusting for the number of independent 
variables in the model. The adjusted R-squared of the IPS period model was 0.1894, indicating that 
almost 19% of relative payment weight variation was accounted for by the independent variables in 
the model. The adjusted R-squared of the 2008 model was 0.1023. The goodness of fit for the 2008 
model does not appear as strong as that of the original model. However, it should be noted that the 
two different R-squared statistics are not directly comparable with one another because the dependent 
variable has changed somewhat (the 80-HHRG casemix in the original model and the 153-HHRG 
casemix in the 2008 model). Also, the 2008 model has dropped independent variables on living 
arrangement because of substantial missing data in the OASIS assessments. 

 

While the models are not intended for the interpretation of individual coefficients, we did examine 
coefficients for the two models to assess the extent to which the coefficients for key drivers of real 
case-mix change were similar. Focusing on the 25 variables associated with the largest change in 
predicted case-mix, we found that: 

 

. Fifteen variables were among the top 25 drivers of case-mix change in both models. 




 

. Of the 25 variables associated with the largest change in predicted case-mix for the IPS-2007 
period  2007, 20 of the variables had the same sign in the 2008 model 




 

. The correlation between the two sets of regression coefficients for the 25 variables associated 
with the largest change in predicted case-mix for the IPS-2007 was 0.74. 




 

These analyses suggest that the results produced by the two models are similar, particularly for the 
key drivers of real case-mix change. 

 

4.3. Regression Coefficients 




Because of the large number of independent variables used in these models, including the use of 
many interaction terms, the potential presence of multicollinearity means that the interpretation of 
individual regression coefficients should be approached with caution, as we have an imprecise 
estimate of the impact of independent changes in covariates. In a context where our goal is to predict 
the dependent variable, multicollinearity is not a problem because the predictions remain accurate. 
Nonetheless, there are several key model results worth noting: 

 

Utilization in period preceding home health episode: In both regression models, the coefficients on 
the variables indicating the number of days of care in each setting in the 14 days preceding the home 
health episode and in the period 15 to 120 days prior were all positive and significant. This implies 


that having more days of care in these settings is associated with higher relative payment weights 
during the home health episode. In addition, the coefficients for the variables for days of care in the 
14 days immediately preceding the home health episode were higher than those for the variables for 
days of care in the earlier period. Such a finding indicates that more-recent days of care in acute care 
hospital, long-term care hospital, rehabilitation facility, and SNF settings have a greater impact on the 
home health episodes relative payment weight. 

Patients living arrangements: The living arrangement variables were included in the IPS model but 
not the 2008 model. Relative to the reference category (those living with a friend), individuals living 
alone had a significantly lower relative payment weight, on average, while those living with a spouse, 
other family members, paid help, or someone else had higher relative payment weights. The 
coefficients for living alone (-0.07267) and living with paid help (0.12521) were particularly 
interesting, in part because they identify the living arrangements associated with the lowest average 
case-mix (living alone) and highest average case-mix (living with paid help), after controlling for the 
other independent variables in the model. One possible explanation is a self-selection effect. 
Individuals with the lowest care needs are able and choose to live alone (assuming these individuals 
do not have a living spouse). Conversely, individuals with greater care needs may have already hired 
live-in help to provide custodial care and services. 

Hospital inpatient history: Most of the individual APR DRG variables were not significant. Note 
that the analysis was not intended to identify and explain all individual effects of APR DRGs on 
home health episode relative payment weights. There are far too many variables, and interpreting 
them is complicated, given the inclusion of APR DRG and severity interactions, as well as the basic 
classification into either a medical APR DRG or a procedure APR DRG. That is, any measured 
impact of an APR DRG is understood to be relative to its basic classification. The purpose of 
including these variables was to capture the impact of the type and severity of an individuals most 
recent acute care hospital stay preceding the home health episode, after accounting for all other 
effects in the model. 

Agency type: Relative to agencies for which the agency type is unknown, relative payment weights 
were lower at freestanding voluntary/non-profit agencies and also lower for facility-based 
government facilities. For the IPS model, relative payment weights were lower for other proprietary 
agencies. In the 2008 model, the opposite pattern was observedrelative payment weights were 
higher for other proprietary agencies. 

Medicare payment amount: Adjusting for the other variables in the model, in both the IPS and 2008 
models, there was a negative relationship between relative payment weight and acute care hospital 
payments in the 120 days preceding the home health episode and a positive relationship between 
relative payment weight and Medicare payments for rehabilitation facilities, and skilled nursing 
facilities. The coefficient for long-term care hospitals was close to zero in both models, but was 
positive for the IPS model and negative for the 2008 model. Each $1,000 increase in payments was 
associated with the following change in case-mix: 

. Acute care hospital: -0.00206 (IPS) -0.00194 (2008) 


. Long-term hospital: 0.00024 (IPS) 0.00700 (2008) 


. Rehabilitation facility: 0.00199 (IPS) 0.00329 (2008) 


. SNF: 0.00915 (IPS) 0.00131 (2008) 




 


The negative coefficient on the acute care hospital expenditures measure may be because the model 
already includes variables that could be related to inpatient payments  e.g., variables for stays and 
days of care in each care setting, as well as APR DRG data for the most recent acute care hospital 
stay. Given the large number of independent variables in the models, it is difficult to interpret the 
coefficients on the payment variables. One possibility is that these variables, when added to the 
model alongside the related variables, might be a further measure of intensity of service  i.e., the 
amount of service provided per day. If services are more intensive in other settings, particularly acute 
care hospital settings, care needs following acute care stays in the home health setting could be lower. 
This result may not be surprising given that research conducted to support the development of the 
case-mix system found that hospital discharges were not associated with higher resource use in home 
health. As a result, in CMSs 80-group system, a hospital discharge did not result in a higher case-
mix weight whereas discharges from skilled nursing or rehabilitation stays did result in a higher case-
mix weight. 

 

4.4. Analysis of Case-Mix Change 




We calculated predicted case-mix values for 2007 using results from the IPS period and 2008 as 
described above. We also calculated the differences between actual case-mix for 2008 and IPS and 
the predicted case-mix values for 2007 and compared these to the actual total change in case-mix that 
occurred during this period. 

 

IPS Period-2007 Case-Mix Change 

Most of the case-mix change that occurred between the IPS period and 2007 was not associated with 
changes in the prevalence of the independent variables included in the regression model and 
presumably reflects changes in nominal factors such as agency coding practices. 

 

. The total change in case-mix between the IPS period and 2007 was 0.1647, with average 
case-mix increasing from 1.0959 to 1.2606 (Table 1). 




 

. Using the IPS model, predicted case-mix for 2007 was 1.1152, an increase of 0.0193 
relative to the IPS period. 




 

. Most of the observed case-mix change between the IPS period and 2007 is nominal change 
that was not predicted by the model. Our estimate is that 88.3% of the case-mix change that 
occurred between the IPS period and 2007 is unpredicted, while 11.7% is predicted (i.e., 
associated with changes in the mean values of covariates between the IPS period and 2007.) 




 

. Our best estimate is that there was a 13.27% nominal increase in case-mix between the IPS 
period and 2007, and a 1.76% real increase in case-mix. 




 

Table 1: 

Summary of Real and Nominal Case-mix Change Estimates: IPS period- 2007 

Measure 

Value 

Average case-mix: IPS period 

1.0959

Average case-mix: 2007 

1.2606




Total change in case-mix 

0.1647

Total percentage change 

15.03%

 

Predicted case-mix (2007 using IPS coefficients) 

1.1152

 

Estimated real (predicted) change in case-mix 

0.0193

Percent of total change estimated as real 

11.70%

Percent of total change estimated as nominal (creep) 

88.30%

Percentage points (of total percentage change) estimated as 
real 

1.76%

Percentage points (of total percentage change) estimated as 
nominal (creep) 

13.27%

Notes: Estimates of real (predicted) case-mix change are based on the sum of case-mix change 
associated with the variables in the model (see the Appendix). Nominal case-mix change is defined as 
the total change in case-mix minus real change in case-mix. 

 

Source: Abt Associates, 2010 



 

2007-2008 Case-Mix Change 

Our estimate of the proportion of case-mix change associated with real factors was lower for 2007-
2008 than it was for the IPS period-2007. This finding is consistent with previous results that have 
shown that the proportion of nominal case-mix change has increased over time. 

 

. The total change in case-mix between 2007 and 2008 was 0.0533, with average case-mix 
increasing from 1.2552 to 1.3085 (Table 2). Note that the 2007 mean case-mix level 
reported in Table 2 differs slightly from that in Table 1 because the mean in Table 2 is based 
on the 153-HHRG model while the mean in Table 1 is based on the 80-HHRG model. The 
change in case-mix between 2007 and 2008 is large, given that this is a one-year difference. 
The 2008 measure coincides with the introduction of the 153-group case mix system. 




 

. Using regression coefficients from the 2008 model, predicted case-mix for 2007 was 1.306, 
indicating that real case-mix in 2008 (1.3085) increased by 0.0025 (1.3085 -1.306 = 0.0025) 
relative to 2007. Our estimate is that 4.7% of the observed case-mix change is real 
(0.0025/0.0533) while the other 95.3% is nominal change ((0.0533  0.0025) / 0.0533) that 
was not predicted by the model. 




 

. Our best estimate is that there was a 3.88% increase in nominal case-mix between 2007 and 
2008 and a 0.19% increase in real case-mix. 




 


Table 2: 

Summary of Real and Nominal Case-mix Change Estimates: 2007-2008 

Measure 

Value

Average case-mix level: 2007 

1.2552

Average case-mix level: 2008 

1.3085

Total change in case-mix 

0.0533

Total percentage change 

4.07%

 

Predicted case-mix (2007 using 2008 coefficients) 

1.3060

 

Estimated real (predicted) change in case-mix 

0.0025

Percent of total change estimated as real 

4.70%

Percent of total change estimated as nominal (creep) 

95.30%

Percentage points (of total percentage change) estimated as 
real 

0.19%

Percentage points (of total percentage change) estimated as 
nominal (creep) 

3.88%

Notes: Estimates of real (predicted) case-mix are based on the sum of case-mix change associated 
with the variables in the model (see the Appendix). Nominal case-mix is defined as the total change in 
case-mix minus real change in case-mix. 

 

Source: Abt Associates, 2010 



 

 

Combining results from Tables 1 and 2, we calculated the total amount of real and nominal change in 
case-mix from the IPS period through 2008, using the methodology described in Section 3. We 
summarize our results in Table 3. 

 

. The total change in case-mix between the IPS period and 2008 was 0.2126 (1.3085-1.0959 = 
0.2126), with average case-mix increasing from 1.0959 to 1.3085, a 19.4% increase. 




 

. Real (predicted) case-mix for 2007 was 1.1152 for 2007 and 1.1173 for 2008. The 1.1173 
estimate is based on the predicted case-mix for 2007 multiplied times the ratio of actual case 
mix in 2008 to predicted case-mix for 2007 (from Table 2). The estimate of all real case-
mix change since the IPS period is 0.0214 (total real case-mix change = 1.95% = 
((1.1173/1.0959)-1)*100%). 




 

. Our estimate is that 10.07% of the case-mix change that occurred between the IPS period 
and 2008 is predicted (real). This is estimated as the predicted (real) change in case-mix 
between the IPS period and 2008 (0.0214; 1.1173-1.0959 = 0.0214) divided by the actual 
change in case-mix for this period (0.2126; 1.3085-1.0959 = 0.2126), yielding 0.0214 / 
0.2126 = 0.1007 or 10.07%. 




 

. Our estimate is that 89.93% (17.45 percentage points) of the 19.40% case-mix change that 
occurred between the IPS period and 2008 is nominal case-mix change that is not due to 
changes in patient characteristics. 




 

 


Table 3: 

Estimate of Total Nominal Case-mix Change: 2000-2008 

Parameter 

Value 

Actual case-mix 

 

2000 (IPS period) 

1.0959 

2008 

1.3085 

Total change: 2000-2008 

0.2126 

Percent change: 2000-2008 

19.40% 

 

 

Real (predicted) case-mix 

 

2007 (change relative to 2000) 

1.1152 

2008 (change relative to 2000) 

1.1173 

Change in real (predicted) case-mix: 2000-2008 

0.0214 

Percent change in real case-mix: 2000-2008 

1.95% 

 

 

Percent of total case-mix change estimated as real 

10.07% 

Nominal case-mix percentage increase 

17.45% 

Notes: 

1) Estimated 2008 real case-mix is calculated as 2007 real case-mix (1.1152) times the ratio 
of 2008 actual case-mix (1.3085) to 2007 estimated real case-mix (1.3060) (from Table 2) . 

 

2) The percent of total case-mix change estimated as real is calculated as the percentage 
change in real case-mix (1.95%) divided by the percentage change in actual case-mix 
(19.4%). 

 

3) The estimate of nominal case-mix percentage increase is calculated as the percentage 
change in actual case-mix (19.40%) times (1- the percent of total case-mix change estimated 
as real (10.07%). 

 

Source: Abt Associates, 2010 



 

 

4.5. Drivers of Real Case-Mix Change 




Either because their regression coefficient is close to zero, or because there was only a small change 
in mean values relative to the IPS period, most of the variables in the model add or subtract a trivial 
amount to the base year level of average case-mix. For the IPS-2007 model, only 143 out of 902 
variables in the model predict a case-mix increase of more than 0.01% or a decrease of more than 
0.01% relative to case-mix during the IPS period. For the 2008-2007 model, only 30 of the 897 
variables in the model predict a case-mix increase of more than 0.01% or a decrease of more than 
0.01% relative to case-mix during 2008. The smaller number of variables for the 2008-2007 model is 
likely due to the smaller change in means from 2007-2008 compared to IPS-2007. 

 

In this section, we focus on the subset of variables in the model that were associated with real changes 
(either increases or decreases) in predicted (real) case-mix for 2007. In addition to the regression 
coefficients and mean values that were reported in Appendix Table 1, Tables 4 and 5 also include 
information on the real case-mix change predicted by these drivers. 

 

The table is organized by variable category. 

 


. Demographics (age, race, gender): None of the demographic variables in the model led 
to a substantial change in expected case-mix. While the interaction terms used in the 
model complicate interpretation of individual parameter estimates, combined, the 
demographic variables included in the models led to a 0.00043 increase in expected case-
mix for the IPS-2007 period and a 0.000141 decrease for 2007-2008 (Table 4) 




 

. Medicare utilization variables: The Medicare utilization variables tended to be 
associated with higher predicted case-mix (.i.e., their regression coefficients were 
positive), but because the mean values of many of these variables decreased over time, 
the Medicare utilization variables were associated with a prediction of slightly negative 
real case-mix change. For the IPS period-2007, the utilization variables were associated 
with a -0.007288 change in real case-mix; for 2007-0008, they were associated with a -
0.003677 decrease. 




 

. Living arrangements: Changes in the distribution of patients by living arrangement lead 
to a real case-mix increase of 0.002801 between the IPS period and 2007. The increase 
in the proportion of patients that live with paid help, which had a rather high regression 
coefficient (0.12521) was the major case-mix driver among the living arrangement 
variables. Note that the living arrangement variables were not included in the 2008 
model. Our analyses suggest that this exclusion had only a minimal impact on our 
estimate of real case-mix change for 2007-2008, which would have been slightly lower 
had these variables been included. 




 

. APR DRG Type (procedure or medical APR DRG): The proportion of both procedure 
and medical APR DRGs decreased slightly from 2000-2008. These variables had 
negative regression coefficients (with the exception of the medical APR DRG variable in 
the 2008 model). The type of hospital diagnosis variables were associated with a 
0.000313 increase in predicted case-mix for the IPS period-2007 and a -0.000261 
decrease for 2007-2008. 




 

. Mortality risk: Over time, the proportion of patients in the minor and moderate mortality 
risk categories decreased while the proportion in the major risk category increased. The 
decrease in patients in the moderate mortality risk category was associated with an 
increase in expected case-mix, given the negative regression coefficients for these 
variables. However, the increase in prevalence of the major mortality risk categories was 
associated with a prediction of lower case-mix, as this also had a negative coefficient. 
Overall, the mortality risk variables were associated with a 0.003062 increase in 
predicted case-mix for the IPS-2007 period and a 0.000918 increase for 2007-2008. 




 

. Hospital diagnosis (APR DRG) variables: While the majority of variables in the model 
are for APR DRGs, most of these variables had low mean values and/or low regression 
coefficients. As a result, the APR DRG variables had only a small impact on our 
estimates of predicted case-mix. Combined, they led to an increase of 0.000755 for the 
IPS period-2007 and a 0.000329 increase for 2007-2008. 




 

. Agency type of control: The two largest drivers of case-mix change were the other 
proprietary and facility-based Vol/NP variables. The proportion of episodes in other 





proprietary agencies increased by 84.5% between the IPS period and 2007. This variable 
had a negative regression coefficient in the IPS model, leading to lower expected case-
mix in 2007. This was offset by the decrease in the proportion of episodes in facility-
based Vol/NP agencies, which also had a negative regression coefficient in the IPS 
model. Combined, the agency type of control variables in the model led to a real case-
mix change of 0.01228 between the IPS period and 2007 and an increase of 0.004964 for 
2007-2008. 




 

. Medicare cost variables: Combined, the four Medicare cost variables in the model led to 
a slight increase in expected case-mixthey were associated with a 0.006904 increase in 
case-mix for the IPS period-2007 and a 0.000366 increase for 2007-2008. 




 

 

Table 4: 

Drivers of Real Case-Mix Change by Category 

 

Real Case-Mix Change 

Category 

IPS-2007 

2007-2008 

Demographics 

0.000430 

-0.000141 

 Medicare utilization 

-0.007288 

-0.003677 

 Living arrangements 

0.002801 

N/A 

APR DRG type (Medical or 
Procedure) 

0.000313 

-0.000261 

 Mortality risk 

0.003062 

0.000918 

 APR DRG 

0.000755 

0.000329 

 Type of control 

0.012283 

0.004964 

 Medicare costs 

0.006904 

0.000366 

Note: Estimates of real case-mix change in this table are derived from the 
table in the Appendix by summing the real case-mix change associated 
with the category of the variable. 

 

Source: Abt Associates, 2010 



 

 

We also examined the variables in the model that were associated with real changes (either increases 
or decreases) in predicted (real) case-mix for 2007. Table 5 shows the variables associated with the 
largest increase in real case-mix for the IPS-2007 period; Table 6 shows the drivers of real case-mix 
change for 2007-2008. The tables show the regression coefficients, the mean values for the variables, 
and the change in mean. The real case-mix change for each variable is calculated as the change in 
mean times the regression coefficient. 

 

. For both models, the largest driver of case-mix change was ownership type: other proprietary. 
For the IPS-2007 period, there was a large increase in the proportion of episodes for this type 
of agency. Combined with a negative regression coefficient, this increase led to a -0.024 
decrease in real case-mix (Table 5). This was offset by the decrease in the proportion of 
episodes to facility-based Vol/NP agencies, which also had a negative regression coefficient. 
For the 2008 model, this covariate had a positive regression coefficient and the increase in 
means observed between 2007 and 2008 led to a prediction of a 0.0041 increase in real case-
mix (Table 6). For the IPS-2007 period, six of the 15 drivers of real case-mix change were 
measures of agency ownership type. 





 

. Any hospitalization in the 14 days prior to the beginning of the home health episode was 
associated with lower case-mix in both the IPS and 2008 models. The mean of this covariate 
has decreased steadily over time and increased real case-mix in both models (0.0073 for the 
IPS-2007 period and 0.0013 for 2007-2008). 




 

. The number of acute care hospital days in the 14 days preceding the episode was associated 
with higher case-mix. Because of the large decrease in mean hospital days (from 2.258 in the 
IPS period to 1.556 in 2007 and 1.438 in 2008), this variable led to a decrease in real case-
mix. Similarly, acute care hospital days in the 15-120 days preceding the episode also 
lowered real case-mix for the IPS-2007 period and for 2007-2008 because of a decrease in 
mean hospital days combined with a positive regression coefficient. 




 

. There was a substantial decrease in the proportion of patients with APR DRG 045 or 046 
(CVA and preverbal occlusion with or without infarction). For both regression models, this 
covariate had a large positive coefficient, meaning that the change in means led to a decrease 
in real case-mix. This was the only APR DRG variable that was a top driver of case-mix 
change in both models. 




 


 

 

Table 5: 

Drivers of Real Case-Mix Change: IPS-2007 

Sev 

Variable 

Regression 
Coefficient 
(IPS) 

IPS Mean 

2007 
Mean 

Change in 
Mean 

Real Case-
Mix 
Change 

 

Other Proprietary 

-0.09851 

0.292672 

0.539954 

0.247282 

-0.024360 

 

Facility-Based Vol/NP 

-0.14481 

0.299250 

0.136032 

-0.163218 

0.023636 

 

Any Hospital in Prior 14 Days IP 
Claims 

-0.08141 

0.383896 

0.2933124 

-0.090583 

0.007374 

 

Free-Standing Vol/NP 

-0.14221 

0.158493 

0.115547 

-0.042946 

0.006107 

 

Acute Care Hospital Days in 
Period 14 Days Preceding Home 
Health Episode 

0.00782 

2.258505 

1.5558445 

-0.702661 

-0.005495 

Any 

Cva W Infarct/Nonspecific Cva & 
Precerebral Occl W/O Infarct 

0.39495 

0.034957 

0.024172 

-0.010785 

-0.004259 

 

Medicare SNF Payments in 120 
Days Preceding Home Health 
Episode 

0.00000915 

$1,164.79 

$1,620.68 

455.890000 

0.004171 

 

No Hosp/Rehab/SNF in 14 Days 
From Prior IP Claims 

-0.0432 

0.518078 

0.601175 

0.083097 

-0.003590 

 

Acute Care Hospital Days in 
Period 15 to 120 Days Preceding 
Home Health Episode 

0.00405 

4.074083 

3.2934306 

-0.780653 

-0.003162 

 

Facility-Based Government 

-0.153 

0.041200 

0.020685 

-0.020515 

0.003139 

 

Acute Care Hospital Payments in 
120 Days Preceding Home Health 
Episode 

-2.06E-06 

$7,569.96 

$6,159.58 

-1410.38 

0.002905 

 

Rehabilitation Facility Days in 
Period 14 Days Preceding Home 
Health Episode 

0.02284 

0.441972 

0.3163284 

-0.125644 

-0.002870 

 

Free-Standing Government 

-0.13322 

0.038689 

0.018570 

-0.020120 

0.002680 

 

Free-Standing Proprietary 

-0.08207 

0.040565 

0.072878 

0.032313 

-0.002652 

 

Facility-Based Proprietary 

-0.11309 

0.036217 

0.012954 

-0.023262 

0.002631 

Any 

08 Knee Joint Replacement 

0.21463 

0.027612 

0.038163 

0.010551 

0.002265 

This is a subset of the table in the Appendix, which presents complete model results. This table reports all variables associated 
with a change in real case-mix of more than 0.002 or less than -0.002. 

 

Source: Abt Associates, 2010 



 


 

Table 6: 

Drivers of Real Case-Mix Change: 2007-2008 

Sev 

Variable 

Regression 
Coefficient 
(2008) 

2007 
Mean 

2008 
Mean 

Change in 
Mean 

Real Case-
Mix 
Change 

 

Other Proprietary 

0.12947 

0.539954 

0.572082 

0.032128 

0.004160 

 

No Hosp/Rehab/SNF in 14 
Days From Prior IP Claims 

-0.11448 

0.601175 

0.618982 

0.017807 

-0.002039 

 

Any Hospital in Prior 14 Days IP 
Claims 

-0.07891 

0.293312 

0.276575 

-0.016737 

0.001321 

 

Acute Care Hospital Days in 
Period 14 Days Preceding 
Home Health Episode 

0.01062 

1.555845 

1.437848 

-0.117996 

-0.001253 

 

Mortality Risk Level 2 

-0.03992 

0.418781 

0.392296 

-0.026486 

0.001057 

 

Rehabilitation Facility Days in 
Period 14 Days Preceding 
Home Health Episode 

0.03675 

0.316328 

0.293976 

-0.022353 

-0.000821 

 

Acute Care Hospital Days in 
Period 15 to 120 Days 
Preceding Home Health 
Episode 

0.0043 

3.293431 

3.15967 

-0.133761 

-0.000575 

 

Free-Standing Proprietary 

0.1026 

0.072878 

0.077890 

0.005012 

0.000514 

 

Facility-Based Vol/NP 

-0.02465 

0.136032 

0.117245 

-0.018788 

0.000463 

 

Mortality Risk Level 3 

-0.02773 

0.158394 

0.174935 

0.016541 

-0.000459 

 

Acute Care Hospital Payments 
in 120 Days Preceding Home 
Health Episode 

-1.94E-06 

$7,979.46 

$7,753.60 

-225.86 

0.000438 

 

Rehabilitation Facility Days in 
Period 15 to 120 Days 
Preceding Home Health 
Episode 

0.0141 

0.428115 

0.398906 

-0.029209 

-0.000412 

Any 

Cva W Infarct/Nonspecific Cva 
& Precerebral Occl W/O Infarct 

0.38616 

0.024172 

0.023159 

-0.001013 

-0.000391 

 

Medicare Skilled Nursing 
Facility (SNF) Days in Period 15 
to 120 Days Preceding Home 
Health Episode 

0.00459 

3.751428 

3.83376 

0.082332 

0.000378 

 

Mortality Risk Level 1 

-0.06421 

0.250267 

0.245287 

-0.004981 

0.000320 

 

Age 85 to 94 

0.04917 

0.242232 

0.247934 

0.005702 

0.000280 

 

Procedure APR DRG 

0.03973 

0.271464 

0.264983 

-0.006481 

-0.000257 

 

Other Vol/NP 

0.03959 

0.078100 

0.072086 

-0.006014 

-0.000238 

Any 

23 Signs, Symptoms & Other 
Factors Influencing Health 
Status 

0.23715 

0.004897 

0.005743 

0.000847 

0.000201 

This is a subset of the table in the Appendix, which presents complete model results. This table reports all variables associated 
with a change in real case-mix of more than 0.002 or less than -0.002. 

 

Source: Abt Associates, 2010 



 

 


5. Discussion 




Since implementation of the prospective payment system, there has been a steady increase in the 
average case-mix of home health patients. The overall observed case-mix increased by 19.40% 
between 2000 and 2008, with the average relative payment weight increasing from 1.0959 to 1.3085. 
The purpose of the analyses described in this report was to estimate the extent to which the observed 
increases in average case-mix were associated with changes in patient characteristics that reflect real 
case-mix change versus changes in agency coding practices or other nominal factors. We used data 
from the IPS period and 2008 to estimate a regression-based, predictive model of individual case-mix 
weights based on measures of patients demographic characteristics, clinical status, inpatient history, 
and Medicare costs in the time period leading up to their home health episodes. 

 

The regression coefficients from these models were applied to episodes from 2007, allowing 
estimation of how much of the change in observed case-mix is attributable to changes in patient 
characteristics over time. We classified the sources of case-mix change into two major types: 
predicted and unpredicted. Real (or predicted) change is based on the relationship between patient 
characteristics and case-mix (i.e., coefficients from the regression model) and changes in the 
characteristics of patients over time (i.e., the change in mean values of the model covariates). 
Unpredicted (or nominal) change is the portion of case-mix change that cannot be explained by 
changes in patient characteristics. Nominal case-mix change is assumed to reflect differences over 
time in agency coding practices. 

 

Our estimate is that 0.0214 (10.07%) of the overall observed case-mix between the IPS period and 
2008 is real, while the other 0.1912 (89.93%) is nominal. This estimate is consistent with prior 
analyses that have found that only a small proportion of the total change in case-mix is real. With 
each successive sample, the predicted average national case-mix weight has changed very little 
because the variables (such as preadmission location, non-home health Part A Medicare expenditures, 
and inpatient stay classification, as mentioned above) in the model used to predict case-mix remain 
relatively constant over time, may have frequently have offsetting effects among them., and/or not 
have a strong relationship to casemix. At the same time, the actual average case-mix has continued to 
grow steadily. Thus, the gap between the predicted and actual has increased with each successive 
year of data. 

 

Our analyses conclude that there has been a 17.45% nominal increase in case-mix ((19.40%  (1 - 
10.07%))) due to changes in coding practices and documentation rather than to treatment of more 
resource-intensive patients. 

 

 

 

 

 

 


 

Appendix Table 1: Regression Coefficients and Mean Values Used for Calculation of Real and 
Nominal Case-Mix Changes: 2000-2008 

 

Appendix Table 1 

Regression Coefficients and Mean Values Used for Calculation of Real and Nominal Case-Mix Changes: 2000-2008 

 

 

Coefficients 

Means 

Real Case-Mix Change 
(2007) 

APR 
DRG 
Sev 

Level 

Variable 

IPS Period 

2008 

IPS 
Mean 

2007 
Mean 

(IPS Model) 

2007 
Mean 

(2008 model) 

2008 
Mean 

Based on 
IPS 
coefficients 

Based on 
2008 
coefficients 

 

 

 

 

 

 

 

 

 

 

 

Intercept 

1.18258 

1.17607 

1.000000 

1 

1 

1 

1.1825800 

1.17607 

 

Age 65 to 74 

-0.01802 

0.00896 

0.245250 

0.2383028 

0.238303 

0.237272 

0.000125 

-0.000009 

 

Age 75 to 84 

0.00050858 

0.01693 

0.401318 

0.3705565 

0.370557 

0.361021 

-0.000016 

-0.000161 

 

Age 85 to 94 

0.04671 

0.04917 

0.236566 

0.2422321 

0.242232 

0.247934 

0.000265 

0.000280 

 

Age 95+ 

0.09629 

0.03333 

0.024610 

0.0249771 

0.024977 

0.025711 

0.000035 

0.000024 

 

Age 65 to 74 * Male 

-0.00503 

0.01177 

0.092414 

0.0902147 

0.090215 

0.089152 

0.000011 

-0.000013 

 

Age 75 to 84 * Male 

-0.00643 

0.03468 

0.134141 

0.1253233 

0.125323 

0.12296 

0.000057 

-0.000082 

 

Age 85 to 84 * male 

-0.01264 

0.04675 

0.064177 

0.0701629 

0.070163 

0.073048 

-0.000076 

0.000135 

 

Age 95+ * Male 

-0.02836 

0.0568 

0.004875 

0.0051765 

0.005177 

0.005676 

-0.000009 

0.000028 

 

Male 

-0.0086 

-0.03596 

0.339518 

0.3474452 

0.347445 

0.349558 

-0.000068 

-0.000076 

 

Age 65 to 74 * White 

-0.01342 

-0.00299 

0.193385 

0.1769986 

0.176999 

0.175336 

0.000220 

0.000005 

 

Age 75 to 84 * White 

-0.01441 

0.00997 

0.340447 

0.2941894 

0.294189 

0.285603 

0.000667 

-0.000086 

 

Age 85 to 94 * White 

-0.05118 

-0.00839 

0.204121 

0.2047367 

0.204737 

0.209361 

-0.000032 

-0.000039 

 

Age 95+ * White 

-0.09787 

-0.02052 

0.020048 

0.0204016 

0.020402 

0.020986 

-0.000035 

-0.000012 

 

White 

0.01833 

0.04617 

0.823055 

0.7760053 

0.776005 

0.772184 

-0.000862 

-0.000176 

 

Age 65 to 74 * African American 

0.025 

-0.00557 

0.038645 

0.0448771 

0.044877 

0.044612 

0.000156 

0.000001 




 

Age 75 to 84 * African American 

0.04468 

-0.00647 

0.044595 

0.0474105 

0.047411 

0.046599 

0.000126 

0.000005 

 

Age 85 to 94 * African American 

0.00748 

-0.01887 

0.023730 

0.024293 

0.024293 

0.024252 

0.000004 

0.000001 

 

Age 95+ * African American 

-0.02844 

-0.00622 

0.003509 

0.003275 

0.003275 

0.003255 

0.000007 

0.000000 

 

African American 

-0.00638 

0.03418 

0.132396 

0.1551231 

0.155123 

0.156072 

-0.000145 

0.000032 

 

Any Hospital in Prior 14 Days IP 
Claims 

-0.08141 

-0.07891 

0.383896 

0.2933124 

0.293312 

0.276575 

0.007374 

0.001321 

 

Any Rehab in 14 Days Prior from IP 
Claims 

0.0668 

-0.04333 

0.044234 

0.0310788 

0.031079 

0.028591 

-0.000879 

0.000108 

 

Any MCR SNF in 14 Days Prior From 
IP Claims 

0.0283 

0.04329 

0.119577 

0.1181519 

0.118152 

0.115254 

-0.000040 

-0.000125 

 

No Hosp/Rehab/SNF in 14 Days 
From Prior IP Claims 

-0.0432 

-0.11448 

0.518078 

0.601175 

0.601175 

0.618982 

-0.003590 

-0.002039 

 

Acute Care Hospital Days in Period 
14 Days Preceding Home Health 
Episode 

0.00782 

0.01062 

2.258505 

1.5558445 

1.555845 

1.437848 

-0.005495 

-0.001253 

 

Acute Care Hospital Days in Period 
15 to 120 Days Preceding Home 
Health Episode 

0.00405 

0.0043 

4.074083 

3.2934306 

3.293431 

3.15967 

-0.003162 

-0.000575 

 

Long Term Care Hospital Days in 
Period 14 Days Preceding Home 
Health Episode 

0.02171 

0.01906 

0.054150 

0.0599053 

0.059905 

0.054472 

0.000125 

-0.000104 

 

Long Term Care Hospital Days in 
Period 15 to 120 Days Preceding 
Home Health Episode 

0.00418 

0.00255 

0.206123 

0.26206 

0.26206 

0.248927 

0.000234 

-0.000033 

 

Rehabilitation Facility Days in Period 
14 Days Preceding Home Health 
Episode 

0.02284 

0.03675 

0.441972 

0.3163284 

0.316328 

0.293976 

-0.002870 

-0.000821 




 

Rehabilitation Facility Days in Period 
15 to 120 Days Preceding Home 
Health Episode 

0.00718 

0.0141 

0.679488 

0.428115 

0.428115 

0.398906 

-0.001805 

-0.000412 

 

Medicare Skilled Nursing Facility 
(SNF) Days in Period 14 Days 
Preceding Home Health Episode 

0.01278 

0.00745 

1.170081 

1.2425008 

1.242501 

1.226248 

0.000926 

-0.000121 

 

Medicare Skilled Nursing Facility 
(SNF) Days in Period 15 to 120 Days 
Preceding Home Health Episode 

0.00194 

0.00459 

2.775380 

3.7514276 

3.751428 

3.83376 

0.001894 

0.000378 

 

Patient Lives Alone 

-0.07267 

 

0.304597 

0.2938814 

 

 

0.000779 

0.000000 

 

Patient Lives with Other (Not Family, 
Friends, Paid Help or Spouse) 

0.05791 

 

0.014602 

0.0093357 

 

 

-0.000305 

0.000000 

 

Patient Lives with Other Family 

0.06056 

 

0.282976 

0.28083 

 

 

-0.000130 

0.000000 

 

Patient Lives with Paid Help 

0.12521 

 

0.076673 

0.0916579 

 

 

0.001876 

0.000000 

 

Patient Lives with Spouse 

0.04426 

 

0.349507 

0.3626328 

 

 

0.000581 

0.000000 

 

Medical APR DRG 

-0.00756 

-0.01052 

0.609462 

0.5959051 

0.595905 

0.596286 

0.000102 

-0.000004 

 

Procedure APR DRG 

-0.03775 

0.03973 

0.277029 

0.2714636 

0.271464 

0.264983 

0.000210 

-0.000257 

 

Mortality Risk Level 1 (Minor) 

-0.0721 

-0.06421 

0.274601 

0.2502672 

0.250267 

0.245287 

0.001754 

0.000320 

 

Mortality Risk Level 2 (Moderate) 

-0.05438 

-0.03992 

0.454415 

0.4187814 

0.418781 

0.392296 

0.001938 

0.001057 

 

Mortality Risk Level 3 (Major) 

-0.02796 

-0.02773 

0.135841 

0.158394 

0.158394 

0.174935 

-0.000631 

-0.000459 

Any 

Tracheostomy W Long Term 
Mechanical Ventilation W Extensive 
Procedure 

0.3273 

0.33671 

0.000536 

0.000487 

0.000487 

0.000552 

-0.000016 

0.000022 

Major 

 

-0.00117 

-0.03861 

0.000188 

0.000102 

0.000102 

0.000100 

0.000000 

0.000000 

Extreme 

 

-0.12727 

-0.08465 

0.000313 

0.000371 

0.000371 

0.000431 

-0.000007 

-0.000005 




Any 

Tracheostomy W Long Term 
Mechanical Ventilation W/O 
Extensive Procedure 

0.19932 

0.17192 

0.000948 

0.000878 

0.000878 

0.000886 

-0.000014 

0.000001 

Mod 

 

-0.18388 

0.12261 

0.000108 

0.000046 

0.000046 

0.000039 

0.000011 

-0.000001 

Major 

 

0.05043 

-0.04125 

0.000351 

0.000275 

0.000275 

0.000279 

-0.000004 

0.000000 

Any 

01 Craniotomy For Trauma 

-0.01526 

0.17991 

0.000542 

0.000662 

0.000662 

0.000674 

-0.000002 

0.000002 

Minor 

 

0.3377 

-0.102 

0.000309 

0.000372 

0.000372 

0.000321 

0.000021 

0.000005 

Mod 

 

0.35483 

0.26809 

0.000089 

0.000040 

0.000040 

0.000061 

-0.000018 

0.000006 

Major 

 

0.2477 

-0.01433 

0.000108 

0.000183 

0.000183 

0.000187 

0.000018 

0.000000 

Any 

01 Craniotomy Except For Trauma 

0.42073 

0.3872 

0.002351 

0.002198 

0.002198 

0.002075 

-0.000064 

-0.000048 

Minor 

 

-0.13243 

-0.19351 

0.000922 

0.000729 

0.000729 

0.000659 

0.000026 

0.000014 

Mod 

 

-0.09805 

-0.17612 

0.000842 

0.000806 

0.000806 

0.000758 

0.000004 

0.000009 

Major 

 

-0.03669 

-0.13184 

0.000402 

0.000397 

0.000397 

0.000393 

0.000000 

0.000001 

Any 

01 Ventricular Shunt Procedures 

0.39968 

0.20222 

0.000644 

0.000775 

0.000775 

0.000730 

0.000052 

-0.000009 

Minor 

 

0.09766 

0.01107 

0.000182 

0.000179 

0.000179 

0.000180 

0.000000 

0.000000 

Mod 

 

-0.01476 

0.02849 

0.000367 

0.000498 

0.000498 

0.000436 

-0.000002 

-0.000002 

Any 

01 Spinal Procedures 

0.38137 

0.29507 

0.000657 

0.000727 

0.000727 

0.000685 

0.000027 

-0.000012 

Minor 

 

-0.06927 

-0.25133 

0.000195 

0.000157 

0.000157 

0.000168 

0.000003 

-0.000003 

Mod 

 

-0.18271 

-0.11864 

0.000249 

0.000281 

0.000281 

0.000265 

-0.000006 

0.000002 

Major 

 

-0.11748 

0.01089 

0.000166 

0.000208 

0.000208 

0.000204 

-0.000005 

0.000000 

Any 

01 Extracranial Vascular Procedures 

0.36423 

0.25751 

0.003650 

0.003457 

0.003457 

0.003483 

-0.000070 

0.000007 

Minor 

 

-0.2569 

-0.27757 

0.001200 

0.001157 

0.001157 

0.001085 

0.000011 

0.000020 

Mod 

 

-0.17653 

-0.23155 

0.001694 

0.001509 

0.001509 

0.001480 

0.000033 

0.000007 




Major 

 

-0.14735 

-0.12151 

0.000660 

0.000677 

0.000677 

0.000771 

-0.000002 

-0.000011 

Any 

01 Other Nervous System & Related 
Procedures 

0.23396 

0.19363 

0.000928 

0.000972 

0.000972 

0.000813 

0.000010 

-0.000031 

Minor 

 

0.01026 

-0.09039 

0.000131 

0.000184 

0.000184 

0.000109 

0.000001 

0.000007 

Mod 

 

0.0677 

-0.0539 

0.000450 

0.000348 

0.000348 

0.000351 

-0.000007 

0.000000 

Major 

 

0.12801 

0.01779 

0.000338 

0.000382 

0.000382 

0.000311 

0.000006 

-0.000001 

Any 

01 Spinal Disorders & Injuries 

0.29678 

0.02725 

0.000294 

0.000254 

0.000254 

0.000275 

-0.000012 

0.000001 

Mod 

 

0.10278 

0.33306 

0.000166 

0.000128 

0.000128 

0.000139 

-0.000004 

0.000003 

Major 

 

0.06315 

0.4745 

0.000102 

0.000094 

0.000094 

0.000091 

0.000000 

-0.000002 

Any 

01 Nervous System Malignancy 

-0.08084 

-0.23682 

0.000916 

0.000582 

0.000582 

0.000492 

0.000027 

0.000021 

Minor 

 

0.27972 

0.47043 

0.000089 

0.000051 

0.000051 

0.000033 

-0.000011 

-0.000008 

Mod 

 

0.27316 

0.36231 

0.000421 

0.000250 

0.000250 

0.000195 

-0.000047 

-0.000020 

Major 

 

0.12755 

0.35261 

0.000396 

0.000264 

0.000264 

0.000245 

-0.000017 

-0.000006 

Any 

01 Degenerative Nervous System 
Disorders Exc Mult Sclerosis 

0.36428 

0.26453 

0.004715 

0.006806 

0.006806 

0.006670 

0.000762 

-0.000036 

Minor 

 

-0.18549 

0.00505 

0.000912 

0.000652 

0.000652 

0.000591 

0.000048 

0.000000 

Mod 

 

-0.15438 

-0.11661 

0.002833 

0.004603 

0.004603 

0.004493 

-0.000273 

0.000013 

Major 

 

-0.13009 

-0.06934 

0.000881 

0.001472 

0.001472 

0.001459 

-0.000077 

0.000001 

Any 

01 Multiple Sclerosis & Other 
Demyelinating Diseases 

0.58785 

0.25065 

0.001324 

0.001216 

0.001216 

0.001206 

-0.000063 

-0.000003 

Minor 

 

-0.24667 

0.09776 

0.000491 

0.000304 

0.000304 

0.000303 

0.000046 

0.000000 

Mod 

 

-0.28785 

0.10968 

0.000692 

0.000752 

0.000752 

0.000709 

-0.000017 

-0.000005 

Major 

 

-0.15219 

0.10542 

0.000137 

0.000153 

0.000153 

0.000173 

-0.000002 

0.000002 




Any 

01 Intracranial Hemorrhage 

0.25023 

0.33495 

0.002868 

0.002413 

0.002413 

0.002588 

-0.000114 

0.000058 

Minor 

 

0.04772 

-0.17065 

0.000577 

0.000353 

0.000353 

0.000386 

-0.000011 

-0.000006 

Mod 

 

0.06663 

-0.01829 

0.001327 

0.001007 

0.001007 

0.001011 

-0.000021 

0.000000 

Major 

 

0.09628 

0.00049387 

0.000845 

0.000907 

0.000907 

0.000998 

0.000006 

0.000000 

Any 

Cva W Infarct/Nonspecific Cva & 
Precerebral Occl W/O Infarct 

0.39495 

0.38616 

0.034957 

0.024172 

0.024172 

0.023159 

-0.004259 

-0.000391 

Minor 

 

-0.07792 

-0.17696 

0.003548 

0.001982 

0.001982 

0.001625 

0.000122 

0.000063 

Mod 

 

-0.07325 

-0.07746 

0.022527 

0.014909 

0.014909 

0.013922 

0.000558 

0.000076 

Major 

 

-0.06912 

-0.06044 

0.008391 

0.006657 

0.006657 

0.006850 

0.000120 

-0.000012 

Any 

01 Transient Ischemia 

-0.05165 

0.10762 

0.010952 

0.009199 

0.009199 

0.008699 

0.000091 

-0.000054 

Minor 

 

0.21585 

0.00855 

0.001921 

0.001258 

0.001258 

0.001095 

-0.000143 

-0.000001 

Mod 

 

0.23145 

0.0424 

0.007306 

0.005990 

0.005990 

0.005735 

-0.000305 

-0.000011 

Major 

 

0.17389 

0.0162 

0.001704 

0.001887 

0.001887 

0.001773 

0.000032 

-0.000002 

Any 

01 Peripheral, Cranial & Autonomic 
Nerve Disorders 

-0.16514 

-0.06692 

0.003666 

0.003287 

0.003287 

0.003278 

0.000062 

0.000001 

Minor 

 

0.34645 

0.2768 

0.000507 

0.000408 

0.000408 

0.000460 

-0.000034 

0.000014 

Mod 

 

0.26553 

0.18874 

0.001780 

0.001508 

0.001508 

0.001444 

-0.000072 

-0.000012 

Major 

 

0.31229 

0.21246 

0.001330 

0.001283 

0.001283 

0.001272 

-0.000015 

-0.000002 

Any 

01 Bacterial & Tuberculous Infections 
Of Nervous System 

0.18768 

0.01098 

0.000262 

0.000218 

0.000218 

0.000265 

-0.000008 

0.000001 

Mod 

 

0.09716 

0.14752 

0.000147 

0.000074 

0.000074 

0.000108 

-0.000007 

0.000005 

Major 

 

-0.06652 

0.23401 

0.000096 

0.000083 

0.000083 

0.000107 

0.000001 

0.000006 

Any 

01 Non-Bacterial Infections Of 
Nervous System Exc Viral Meningitis 

-0.09775 

0.08273 

0.000412 

0.000410 

0.000410 

0.000427 

0.000000 

0.000001 




Minor 

 

-0.02908 

-0.0381 

0.000108 

0.000114 

0.000114 

0.000131 

0.000000 

-0.000001 

Mod 

 

0.22816 

0.06563 

0.000140 

0.000141 

0.000141 

0.000132 

0.000000 

-0.000001 

Major 

 

0.3793 

0.1688 

0.000140 

0.000115 

0.000115 

0.000127 

-0.000010 

0.000002 

Any 

01 Nontraumatic Stupor & Coma 

0.18585 

0.14078 

0.001694 

0.002989 

0.002989 

0.003327 

0.000241 

0.000048 

Minor 

 

-0.12804 

-0.059 

0.000191 

0.000160 

0.000160 

0.000168 

0.000004 

0.000000 

Mod 

 

-0.03121 

-0.03867 

0.000699 

0.000726 

0.000726 

0.000690 

-0.000001 

0.000001 

Major 

 

-0.05085 

0.01348 

0.000766 

0.001929 

0.001929 

0.002229 

-0.000059 

0.000004 

Any 

01 Seizure 

0.13094 

0.04413 

0.004770 

0.004952 

0.004952 

0.004934 

0.000024 

-0.000001 

Minor 

 

-0.0945 

0.04621 

0.000676 

0.000576 

0.000576 

0.000650 

0.000009 

0.000003 

Mod 

 

0.03536 

0.07491 

0.002686 

0.002636 

0.002636 

0.002548 

-0.000002 

-0.000007 

Major 

 

-0.04479 

0.08566 

0.001257 

0.001514 

0.001514 

0.001516 

-0.000012 

0.000000 

Any 

01 Migraine & Other Headaches 

0.02372 

-0.00436 

0.000523 

0.000703 

0.000703 

0.000716 

0.000004 

0.000000 

Minor 

 

0.01025 

0.21441 

0.000134 

0.000142 

0.000142 

0.000157 

0.000000 

0.000003 

Mod 

 

0.15649 

0.06133 

0.000306 

0.000448 

0.000448 

0.000454 

0.000022 

0.000000 

Any 

01 Head Trauma W Coma >1 Hr Or 
Hemorrhage 

0.39013 

0.21446 

0.000900 

0.002050 

0.002050 

0.002225 

0.000449 

0.000037 

Minor 

 

-0.03567 

-0.05245 

0.000144 

0.000241 

0.000241 

0.000279 

-0.000003 

-0.000002 

Mod 

 

-0.17407 

-0.000158 

0.000472 

0.001115 

0.001115 

0.001226 

-0.000112 

0.000000 

Major 

 

-0.11597 

-0.07163 

0.000242 

0.000581 

0.000581 

0.000630 

-0.000039 

-0.000004 

Any 

01 Brain Contusion/Laceration & 
Complicated Skull Fx, Coma < 1 Hr 
Or No Coma 

0.45473 

0.185 

0.000357 

0.000468 

0.000468 

0.000508 

0.000050 

0.000007 

Mod 

 

-0.23255 

-0.03522 

0.000220 

0.000265 

0.000265 

0.000292 

-0.000010 

-0.000001 




Major 

 

-0.40577 

-0.04994 

0.000083 

0.000117 

0.000117 

0.000119 

-0.000014 

0.000000 

Any 

01 Concussion, Closed Skull Fx 
NOS, Uncomplicated Intracranial 
Injury, Coma < 1 Hr Or No Coma 

-0.01457 

-0.03162 

0.000536 

0.000762 

0.000762 

0.000826 

-0.000003 

-0.000002 

Minor 

 

0.18334 

0.22665 

0.000096 

0.000075 

0.000075 

0.000094 

-0.000004 

0.000004 

Mod 

 

0.13346 

0.18574 

0.000316 

0.000481 

0.000481 

0.000516 

0.000022 

0.000006 

Major 

 

0.09551 

0.14919 

0.000115 

0.000192 

0.000192 

0.000199 

0.000007 

0.000001 

Any 

01 Other Disorders Of Nervous 
System 

0.27138 

0.31645 

0.003934 

0.004676 

0.004676 

0.004681 

0.000201 

0.000001 

Minor 

 

-0.05643 

-0.13934 

0.001662 

0.002053 

0.002053 

0.001924 

-0.000022 

0.000018 

Mod 

 

-0.02672 

-0.08878 

0.001640 

0.001873 

0.001873 

0.001835 

-0.000006 

0.000003 

Major 

 

-0.08349 

-0.04646 

0.000609 

0.000681 

0.000681 

0.000813 

-0.000006 

-0.000006 

Any 

02 Eye Procedures Except Orbit 

0.0316 

-0.08326 

0.000415 

0.000148 

0.000148 

0.000179 

-0.000008 

-0.000003 

Minor 

 

0.03056 

0.03014 

0.000134 

0.000057 

0.000057 

0.000054 

-0.000002 

0.000000 

Mod 

 

0.18053 

0.25115 

0.000223 

0.000071 

0.000071 

0.000103 

-0.000028 

0.000008 

Any 

02 Acute Major Eye Infections 

0.18497 

-0.05486 

0.000166 

0.000201 

0.000201 

0.000196 

0.000006 

0.000000 

Mod 

 

-0.02851 

0.07818 

0.000089 

0.000123 

0.000123 

0.000139 

-0.000001 

0.000001 

Any 

02 Eye Disorders Except Major 
Infections 

0.11621 

0.15567 

0.000392 

0.000486 

0.000486 

0.000454 

0.000011 

-0.000005 

Mod 

 

-0.05748 

-0.03892 

0.000246 

0.000277 

0.000277 

0.000245 

-0.000002 

0.000001 

Major 

 

-0.08336 

-0.03987 

0.000093 

0.000130 

0.000130 

0.000123 

-0.000003 

0.000000 

Any 

03 Major Cranial/Facial Bone 
Procedures 

0.18856 

0.15336 

0.000278 

0.000231 

0.000231 

0.000218 

-0.000009 

-0.000002 

Major 

 

-0.07385 

-0.20696 

0.000175 

0.000134 

0.000134 

0.000128 

0.000003 

0.000001 




0.000157 

0.000186 

-0.000009 

-0.000004 

Mod 

 

-0.01987 

0.06787 

0.000144 

0.000075 

0.000075 

0.000077 

0.000001 

0.000000 

Any 

03 Facial Bone Procedures Except 
Major Cranial/Facial Bone 
Procedures 

0.12438 

0.02625 

0.000156 

0.000099 

0.000099 

0.000094 

-0.000007 

0.000000 

Mod 

 

0.12151 

-0.12247 

0.000080 

0.000039 

0.000039 

0.000048 

-0.000005 

-0.000001 

Any 

03 Other Ear, Nose, Mouth & Throat 
Procedures 

0.05519 

-0.18833 

0.000558 

0.000390 

0.000390 

0.000397 

-0.000009 

-0.000001 

Minor 

 

-0.02432 

0.08374 

0.000160 

0.000087 

0.000087 

0.000095 

0.000002 

0.000001 

Mod 

 

-0.06385 

0.13539 

0.000274 

0.000173 

0.000173 

0.000167 

0.000006 

-0.000001 

Major 

 

-0.122 

0.0394 

0.000096 

0.000103 

0.000103 

0.000086 

-0.000001 

-0.000001 

Any 

03 Ear, Nose, Mouth, Throat, 
Cranial/Facial Malignancies 

-0.03748 

-0.13047 

0.000284 

0.000248 

0.000248 

0.000251 

0.000001 

0.000000 

Mod 

 

-0.03105 

0.07781 

0.000086 

0.000067 

0.000067 

0.000068 

0.000001 

0.000000 

Major 

 

0.01864 

0.11833 

0.000128 

0.000126 

0.000126 

0.000134 

0.000000 

0.000001 

Any 

03 Vertigo & Other Labyrinth 
Disorders 

-0.03939 

0.11874 

0.002061 

0.003018 

0.003018 

0.002823 

-0.000038 

-0.000023 

Minor 

 

0.08128 

-0.11175 

0.000609 

0.000810 

0.000810 

0.000675 

0.000016 

0.000015 

Mod 

 

0.10758 

-0.06636 

0.001228 

0.001780 

0.001780 

0.001754 

0.000059 

0.000002 

Any 

03 Infections Of Upper Respiratory 
Tract 

-0.38314 

0.06676 

0.001299 

0.001099 

0.001099 

0.001566 

0.000077 

0.000031 

Minor 

 

0.39849 

-0.06196 

0.000160 

0.000123 

0.000123 

0.000124 

-0.000015 

0.000000 

Appendix Table 1 

Regression Coefficients and Mean Values Used for Calculation of Real and Nominal Case-Mix Changes: 2000-2008 

 

 

Coefficients 

Means 

Real Case-Mix Change 
(2007) 

APR 
DRG 
Sev 

Level 

Variable 

IPS Period 

2008 

IPS 
Mean 

2007 
Mean 

(IPS Model) 

2007 
Mean 

(2008 model) 

Based on 
IPS 
coefficients 

Based on 
2008 
coefficients 

Any 

03 Major Larynx & Trachea 
Procedures 

0.01359 

0.04716 

0.000389 

0.000187 

0.000187 

-0.000003 

0.000002 

Mod 

 

-0.03584 

-0.08335 

0.000306 

0.000145 

0.000145 

0.000006 

0.000000 

Any 

03 Other Major Head & Neck 
Procedures 

0.10069 

-0.12702 

0.000242 

0.000157 



2008 
Mean 

0.000220 

0.000139 


Appendix Table 1 

Regression Coefficients and Mean Values Used for Calculation of Real and Nominal Case-Mix Changes: 2000-2008 

 

 

Coefficients 

Means 

Real Case-Mix Change 
(2007) 

APR 
DRG 
Sev 

Level 

Variable 

IPS Period 

2008 

IPS 
Mean 

2007 
Mean 

(IPS Model) 

2007 
Mean 

(2008 model) 

Based on 
IPS 
coefficients 

Based on 
2008 
coefficients 

Mod 

 

0.3867 

-0.00604 

0.000871 

0.000666 

0.000666 

0.000923 

-0.000079 

-0.000002 

Major 

 

0.4361 

-0.01197 

0.000258 

0.000292 

0.000292 

0.000493 

0.000015 

-0.000002 

Any 

03 Dental & Oral Diseases & Injuries 

-0.0556 

-0.0174 

0.000287 

0.000434 

0.000434 

0.000516 

-0.000008 

-0.000001 

Mod 

 

0.1599 

0.13972 

0.000185 

0.000237 

0.000237 

0.000275 

0.000008 

0.000005 

Any 

03 Other Ear, Nose, Mouth,Throat & 
Cranial/Facial Diagnoses 

-0.03881 

0.1418 

0.001263 

0.001655 

0.001655 

0.001764 

-0.000015 

0.000015 

Minor 

 

-0.00587 

-0.05888 

0.000376 

0.000508 

0.000508 

0.000499 

-0.000001 

0.000001 

Mod 

 

0.1169 

-0.03705 

0.000625 

0.000856 

0.000856 

0.000900 

0.000027 

-0.000002 

Major 

 

0.0894 

0.09957 

0.000217 

0.000233 

0.000233 

0.000288 

0.000001 

0.000005 

Any 

04 Major Respiratory & Chest 
Procedures 

0.03143 

0.02537 

0.001940 

0.002110 

0.002110 

0.001993 

0.000005 

-0.000003 

Minor 

 

-0.07511 

-0.13602 

0.000294 

0.000229 

0.000229 

0.000195 

0.000005 

0.000005 

Mod 

 

-0.07645 

-0.08735 

0.000970 

0.000981 

0.000981 

0.000928 

-0.000001 

0.000005 

Major 

 

-0.06678 

-0.02315 

0.000533 

0.000637 

0.000637 

0.000595 

-0.000007 

0.000001 

Any 

04 Other Respiratory & Chest 
Procedures 

0.06319 

-0.09625 

0.001793 

0.001688 

0.001688 

0.001747 

-0.000007 

-0.000006 

Minor 

 

-0.10817 

-0.03993 

0.000309 

0.000192 

0.000192 

0.000197 

0.000013 

0.000000 

Mod 

 

-0.11261 

0.01533 

0.000814 

0.000733 

0.000733 

0.000708 

0.000009 

0.000000 

Major 

 

-0.08622 

0.06693 

0.000495 

0.000545 

0.000545 

0.000597 

-0.000004 

0.000004 

Any 

04 Respiratory System Diagnosis W 
Ventilator Support 96+ Hours 

0.18301 

-0.03535 

0.002855 

0.002018 

0.002018 

0.001921 

-0.000153 

0.000003 

Mod 

 

-0.10922 

0.07941 

0.000501 

0.000223 

0.000223 

0.000201 

0.000030 

-0.000002 

Major 

 

-0.16609 

0.12826 

0.001372 

0.000823 

0.000823 

0.000657 

0.000091 

-0.000021 

Extreme 

 

-0.1019 

0.11415 

0.000928 

0.000956 

0.000956 

0.001041 

-0.000003 

0.000010 



2008 
Mean 


Appendix Table 1 

Regression Coefficients and Mean Values Used for Calculation of Real and Nominal Case-Mix Changes: 2000-2008 

 

 

Coefficients 

Means 

Real Case-Mix Change 
(2007) 

APR 
DRG 
Sev 

Level 

Variable 

IPS Period 

2008 

IPS 
Mean 

2007 
Mean 

(IPS Model) 

2007 
Mean 

(2008 model) 

Based on 
IPS 
coefficients 

Based on 
2008 
coefficients 

Any 

04 Pulmonary Edema & Respiratory 
Failure 

-0.04014 

0.0063 

0.006196 

0.009301 

0.009301 

0.010485 

-0.000125 

0.000007 

Minor 

 

-0.0328 

0.13241 

0.000124 

0.000030 

0.000030 

0.000025 

0.000003 

-0.000001 

Mod 

 

-0.0593 

-0.00534 

0.001452 

0.001320 

0.001320 

0.001559 

0.000008 

-0.000001 

Major 

 

-0.02843 

0.02465 

0.002632 

0.004333 

0.004333 

0.005085 

-0.000048 

0.000019 

Any 

04 Pulmonary Embolism 

-0.10157 

0.06686 

0.003407 

0.005768 

0.005768 

0.005645 

-0.000240 

-0.000008 

Minor 

 

-0.00229 

-0.14798 

0.000392 

0.000632 

0.000632 

0.000530 

-0.000001 

0.000015 

Mod 

 

0.09668 

-0.08123 

0.001678 

0.002666 

0.002666 

0.002587 

0.000095 

0.000006 

Major 

 

0.05564 

-0.02409 

0.001158 

0.002172 

0.002172 

0.002144 

0.000056 

0.000001 

Any 

04 Major Chest & Respiratory 
Trauma 

0.00141 

0.10507 

0.001388 

0.001461 

0.001461 

0.001545 

0.000000 

0.000009 

Minor 

 

0.06772 

-0.023 

0.000536 

0.000482 

0.000482 

0.000515 

-0.000004 

-0.000001 

Mod 

 

0.13911 

0.01472 

0.000437 

0.000458 

0.000458 

0.000484 

0.000003 

0.000000 

Major 

 

0.06419 

0.02407 

0.000370 

0.000450 

0.000450 

0.000470 

0.000005 

0.000000 

Any 

04 Respiratory Malignancy 

-0.12515 

-0.05971 

0.003130 

0.002194 

0.002194 

0.001849 

0.000117 

0.000021 

Minor 

 

0.10583 

-0.11736 

0.000124 

0.000085 

0.000085 

0.000057 

-0.000004 

0.000003 

Mod 

 

0.00191 

-0.0141 

0.001375 

0.000764 

0.000764 

0.000572 

-0.000001 

0.000003 

Major 

 

-0.00563 

-0.01243 

0.001519 

0.001221 

0.001221 

0.001084 

0.000002 

0.000002 

Any 

04 Major Respiratory Infections & 
Inflammations 

0.1555 

0.13195 

0.014127 

0.009881 

0.009881 

0.010087 

-0.000660 

0.000027 

Minor 

 

-0.17445 

-0.08429 

0.000587 

0.000253 

0.000253 

0.000282 

0.000058 

-0.000002 

Mod 

 

-0.05159 

-0.01675 

0.005580 

0.003430 

0.003430 

0.003224 

0.000111 

0.000003 

Major 

 

0.01144 

0.01753 

0.006646 

0.004894 

0.004894 

0.004916 

-0.000020 

0.000000 



2008 
Mean 


Appendix Table 1 

Regression Coefficients and Mean Values Used for Calculation of Real and Nominal Case-Mix Changes: 2000-2008 

 

 

Coefficients 

Means 

Real Case-Mix Change 
(2007) 

APR 
DRG 
Sev 

Level 

Variable 

IPS Period 

2008 

IPS 
Mean 

2007 
Mean 

(IPS Model) 

2007 
Mean 

(2008 model) 

Based on 
IPS 
coefficients 

Based on 
2008 
coefficients 

Any 

04 Other Pneumonia 

-0.0381 

0.05789 

0.044333 

0.037104 

0.037104 

0.034990 

0.000275 

-0.000122 

Minor 

 

0.02881 

-0.05164 

0.002275 

0.001756 

0.001756 

0.001730 

-0.000015 

0.000001 

Mod 

 

0.0336 

-0.0189 

0.023222 

0.018169 

0.018169 

0.016622 

-0.000170 

0.000029 

Major 

 

0.04181 

-0.02454 

0.017375 

0.015593 

0.015593 

0.014613 

-0.000074 

0.000024 

Any 

04 Chronic Obstructive Pulmonary 
Disease 

-0.10151 

-0.04399 

0.029275 

0.025214 

0.025214 

0.028926 

0.000412 

-0.000163 

Minor 

 

0.01143 

-0.00442 

0.006256 

0.003857 

0.003857 

0.003626 

-0.000027 

0.000001 

Mod 

 

0.03585 

0.03018 

0.014899 

0.012535 

0.012535 

0.013593 

-0.000085 

0.000032 

Major 

 

0.01786 

0.03265 

0.007143 

0.007796 

0.007796 

0.010372 

0.000012 

0.000084 

Any 

04 Asthma 

0.04547 

0.28419 

0.002300 

0.001761 

0.001761 

0.001901 

-0.000025 

0.000040 

Minor 

 

-0.04726 

-0.3034 

0.000396 

0.000258 

0.000258 

0.000270 

0.000006 

-0.000004 

Mod 

 

-0.12376 

-0.295 

0.001378 

0.001044 

0.001044 

0.001154 

0.000041 

-0.000032 

Major 

 

-0.07255 

-0.28568 

0.000507 

0.000437 

0.000437 

0.000445 

0.000005 

-0.000002 

Any 

04 Interstitial Lung Disease 

-0.0996 

0.19013 

0.001273 

0.001171 

0.001171 

0.001129 

0.000010 

-0.000008 

Mod 

 

0.0509 

-0.16608 

0.000561 

0.000501 

0.000501 

0.000454 

-0.000003 

0.000008 

Major 

 

0.11287 

-0.20893 

0.000577 

0.000561 

0.000561 

0.000539 

-0.000002 

0.000005 

Any 

04 Other Respiratory Diagnoses 
Except Signs, Symptoms & Minor 
Diagnoses 

-0.01016 

0.08958 

0.002900 

0.002253 

0.002253 

0.002460 

0.000007 

0.000018 

Minor 

 

0.02987 

0.02246 

0.000223 

0.000142 

0.000142 

0.000104 

-0.000002 

-0.000001 

Mod 

 

0.00153 

-0.07325 

0.001471 

0.001086 

0.001086 

0.001026 

-0.000001 

0.000004 

Major 

 

0.05195 

-0.06942 

0.001011 

0.000825 

0.000825 

0.001065 

-0.000010 

-0.000017 

Any 

04 Respiratory Signs, Symptoms & 
Minor Diagnoses 

0.23861 

0.12102 

0.006604 

0.006141 

0.006141 

0.006539 

-0.000111 

0.000048 



2008 
Mean 


Appendix Table 1 
-0.19844 

Regression Coefficients and Mean Values Used for Calculation of Real and Nominal Case-Mix Changes: 2000-2008 
-0.04933 

 
0.003410 

 
0.003410 

Coefficients 
0.003516 

Means 
0.000056 

Real Case-Mix Change 
(2007) 
-0.000005 

Mod 

 

0.003691 

APR 
DRG 
Sev 
Major 

Level 


Variable 
-0.1964 

IPS Period 
-0.06709 

2008 
0.001493 

IPS 
Mean 
0.001395 

2007 
Mean 
0.001395 

(IPS Model) 
0.001606 

2007 
Mean 
0.000019 

(2008 model) 
-0.000014 

Based on 
IPS 
coefficients 
Any 

Based on 
2008 
coefficients 
05 Cardiac Defibrillator & Heart 
Assist Implant 

-0.07126 

-0.12147 

0.001257 

0.003308 

0.003308 

0.003286 

-0.000146 

0.000003 

Minor 

 

-0.22731 

-0.10904 

0.001372 

0.001224 

0.001224 

0.001261 

0.000034 

-0.000004 

Mod 

 

0.07897 

-0.00164 

0.000415 

0.000970 

0.000970 

0.000886 

0.000044 

0.000000 

Major 

 

-0.01013 

0.05112 

0.000613 

0.001880 

0.001880 

0.001882 

-0.000013 

0.000000 

Extreme 

 

0.11118 

0.04235 

0.000153 

0.000330 

0.000330 

0.000369 

0.000020 

0.000002 

Any 

05 Cardiac Valve Procedures W 
Cardiac Catheterization 

-0.01012 

-0.05949 

0.002316 

0.001937 

0.001937 

0.001786 

0.000004 

0.000009 

Minor 

 

-0.10774 

-0.17154 

0.000121 

0.000066 

0.000066 

0.000078 

0.000006 

-0.000002 

Mod 

 

-0.08774 

-0.15223 

0.000597 

0.000369 

0.000369 

0.000334 

0.000020 

0.000005 

Major 

 

-0.05744 

-0.06401 

0.001353 

0.000977 

0.000977 

0.000901 

0.000022 

0.000005 

Any 

05 Cardiac Valve Procedures W/O 
Cardiac Catheterization 

0.0463 

0.0099 

0.003312 

0.003257 

0.003257 

0.003189 

-0.000003 

-0.000001 

Minor 

 

-0.23228 

-0.22444 

0.000297 

0.000221 

0.000221 

0.000211 

0.000018 

0.000002 

Mod 

 

-0.14621 

-0.17531 

0.001257 

0.001035 

0.001035 

0.000887 

0.000032 

0.000026 

Major 

 

-0.13906 

-0.16686 

0.001436 

0.001440 

0.001440 

0.001487 

-0.000001 

-0.000008 

Any 

05 Coronary Bypass W Cardiac Cath 
Or Percutaneous Cardiac Procedure 

0.06255 

-0.06247 

0.011201 

0.006414 

0.006414 

0.005720 

-0.000299 

0.000043 

Minor 

 

-0.19524 

-0.14838 

0.000657 

0.000262 

0.000262 

0.000222 

0.000077 

0.000006 

Mod 

 

-0.16022 

-0.12149 

0.005816 

0.002637 

0.002637 

0.002257 

0.000509 

0.000046 

Major 

 

-0.12918 

-0.07795 

0.003892 

0.002649 

0.002649 

0.002323 

0.000161 

0.000025 



2008 
Mean 


Appendix Table 1 

Regression Coefficients and Mean Values Used for Calculation of Real and Nominal Case-Mix Changes: 2000-2008 

 

 

Coefficients 

Means 

Real Case-Mix Change 
(2007) 

APR 
DRG 
Sev 

Level 

Variable 

IPS Period 

2008 

IPS 
Mean 

2007 
Mean 

(IPS Model) 

2007 
Mean 

(2008 model) 

Based on 
IPS 
coefficients 

Based on 
2008 
coefficients 

Any 

05 Coronary Bypass W/O Cardiac 
Cath Or Percutaneous Cardiac 
Procedure 

-0.03305 

-0.1052 

0.006939 

0.004401 

0.004401 

0.003936 

0.000084 

0.000049 

Minor 

 

-0.12286 

-0.10352 

0.000743 

0.000280 

0.000280 

0.000209 

0.000057 

0.000007 

Mod 

 

-0.07994 

-0.07708 

0.004013 

0.002159 

0.002159 

0.001923 

0.000148 

0.000018 

Major 

 

-0.01555 

-0.04108 

0.001876 

0.001493 

0.001493 

0.001356 

0.000006 

0.000006 

Any 

05 Other Cardiothoracic Procedures 

-0.13653 

-0.08319 

0.000313 

0.000308 

0.000308 

0.000338 

0.000001 

-0.000003 

Major 

 

-0.01263 

0.00334 

0.000163 

0.000149 

0.000149 

0.000152 

0.000000 

0.000000 

Any 

05 Major Thoracic & Abdominal 
Vascular Procedures 

0.03085 

0.0122 

0.003411 

0.001813 

0.001813 

0.001592 

-0.000049 

-0.000003 

Minor 

 

0.01834 

-0.22394 

0.000242 

0.000109 

0.000109 

0.000085 

-0.000002 

0.000005 

Mod 

 

-0.08289 

-0.09934 

0.001445 

0.000670 

0.000670 

0.000630 

0.000064 

0.000004 

Major 

 

-0.02152 

-0.11397 

0.001222 

0.000651 

0.000651 

0.000544 

0.000012 

0.000012 

Any 

05 Permanent Cardiac Pacemaker 
Implant W Ami, Heart Failure Or 
Shock 

-0.13838 

0.03034 

0.001133 

0.000841 

0.000841 

0.000641 

0.000040 

-0.000006 

Minor 

 

0.04907 

-0.17444 

0.000134 

0.000045 

0.000045 

0.000032 

-0.000004 

0.000002 

Mod 

 

0.11044 

-0.07522 

0.000571 

0.000419 

0.000419 

0.000289 

-0.000017 

0.000010 

Major 

 

0.1489 

-0.09156 

0.000386 

0.000315 

0.000315 

0.000260 

-0.000011 

0.000005 

Any 

05 Perm Cardiac Pacemaker Implant 
W/O Ami, Heart Failure Or Shock 

0.18454 

-0.02765 

0.007239 

0.007863 

0.007863 

0.008120 

0.000115 

-0.000007 

Minor 

 

-0.19878 

-0.05436 

0.001914 

0.001829 

0.001829 

0.001882 

0.000017 

-0.000003 

Mod 

 

-0.17207 

-0.001 

0.003921 

0.004195 

0.004195 

0.004174 

-0.000047 

0.000000 

Major 

 

-0.20099 

0.03102 

0.001260 

0.001630 

0.001630 

0.001791 

-0.000074 

0.000005 



2008 
Mean 


Appendix Table 1 

Regression Coefficients and Mean Values Used for Calculation of Real and Nominal Case-Mix Changes: 2000-2008 

 

 

Coefficients 

Means 

Real Case-Mix Change 
(2007) 

APR 
DRG 
Sev 

Level 

Variable 

IPS Period 

2008 

IPS 
Mean 

2007 
Mean 

(IPS Model) 

2007 
Mean 

(2008 model) 

Based on 
IPS 
coefficients 

Based on 
2008 
coefficients 

Any 

05 Other Vascular Procedures DRG 
Med - Surg MDC Long Descriptions 

0.17388 

-0.01169 

0.011488 

0.010260 

0.010260 

0.009976 

-0.000214 

0.000003 

Minor 

 

-0.13183 

-0.0778 

0.002221 

0.001915 

0.001915 

0.001803 

0.000040 

0.000009 

Mod 

 

-0.09287 

-0.0232 

0.004451 

0.003907 

0.003907 

0.003571 

0.000050 

0.000008 

Major 

 

-0.08703 

-0.03517 

0.004013 

0.003452 

0.003452 

0.003482 

0.000049 

-0.000001 

Any 

05 Percutaneous Cardiovascular 
Procedures W Ami 

-0.05866 

-0.06028 

0.002875 

0.004179 

0.004179 

0.003966 

-0.000076 

0.000013 

Minor 

 

0.00838 

-0.01468 

0.000268 

0.000423 

0.000423 

0.000389 

0.000001 

0.000000 

Mod 

 

0.00818 

-0.01282 

0.001397 

0.001894 

0.001894 

0.001748 

0.000004 

0.000002 

Major 

 

0.0112 

0.02068 

0.000715 

0.001221 

0.001221 

0.001168 

0.000006 

-0.000001 

Any 

05 Percutaneous Cardiovascular 
Procedures W/O Ami 

0.05225 

0.0277 

0.005149 

0.007996 

0.007996 

0.007743 

0.000149 

-0.000007 

Minor 

 

-0.06542 

-0.09656 

0.001158 

0.002208 

0.002208 

0.002152 

-0.000069 

0.000005 

Mod 

 

-0.0712 

-0.09253 

0.002450 

0.003439 

0.003439 

0.003185 

-0.000070 

0.000024 

Major 

 

-0.12773 

-0.05881 

0.001209 

0.001924 

0.001924 

0.001947 

-0.000091 

-0.000001 

Any 

05 Cardiac Pacemaker & Defibrillator 
Device Replacement 

0.05205 

0.04228 

0.000555 

0.000769 

0.000769 

0.000814 

0.000011 

0.000002 

Minor 

 

-0.03142 

-0.03369 

0.000399 

0.000457 

0.000457 

0.000465 

-0.000002 

0.000000 

Major 

 

-0.06681 

-0.05453 

0.000118 

0.000223 

0.000223 

0.000244 

-0.000007 

-0.000001 

Any 

05 Cardiac Pacemaker & Defibrillator 
Revision Except Device Replacement 

-0.10606 

-0.09869 

0.000290 

0.000598 

0.000598 

0.000675 

-0.000033 

-0.000008 

Minor 

 

0.01836 

0.07075 

0.000124 

0.000186 

0.000186 

0.000252 

0.000001 

0.000005 

Mod 

 

-0.0966 

-0.0305 

0.000121 

0.000229 

0.000229 

0.000222 

-0.000010 

0.000000 

Any 

05 Other Circulatory System 
Procedures 

0.03398 

0.04813 

0.001927 

0.001265 

0.001265 

0.001169 

-0.000023 

-0.000005 



2008 
Mean 


Appendix Table 1 

Regression Coefficients and Mean Values Used for Calculation of Real and Nominal Case-Mix Changes: 2000-2008 

 

 

Coefficients 

Means 

Real Case-Mix Change 
(2007) 

APR 
DRG 
Sev 

Level 

Variable 

IPS Period 

2008 

IPS 
Mean 

2007 
Mean 

(IPS Model) 

2007 
Mean 

(2008 model) 

Based on 
IPS 
coefficients 

Based on 
2008 
coefficients 

Minor 

 

-0.03879 

-0.18022 

0.000386 

0.000095 

0.000095 

0.000103 

0.000011 

-0.000001 

Mod 

 

-0.01486 

-0.08929 

0.000561 

0.000377 

0.000377 

0.000344 

0.000003 

0.000003 

Major 

 

-0.02025 

-0.05817 

0.000817 

0.000578 

0.000578 

0.000521 

0.000005 

0.000003 

Any 

05 Acute Myocardial Infarction 

-0.04724 

0.01983 

0.013345 

0.009329 

0.009329 

0.009151 

0.000190 

-0.000004 

Minor 

 

-0.02241 

-0.01404 

0.001314 

0.000705 

0.000705 

0.000637 

0.000014 

0.000001 

Mod 

 

-0.02352 

0.01095 

0.005794 

0.003378 

0.003378 

0.003192 

0.000057 

-0.000002 

Major 

 

-0.01039 

0.02498 

0.004878 

0.003859 

0.003859 

0.003831 

0.000011 

-0.000001 

Any 

05 Cardiac Catheterization W Circ 
Disord Exc Ischemic Heart Disease 

-0.14573 

-0.05735 

0.003385 

0.003450 

0.003450 

0.003514 

-0.000010 

-0.000004 

Minor 

 

0.09156 

0.0706 

0.000242 

0.000253 

0.000253 

0.000324 

0.000001 

0.000005 

Mod 

 

0.07185 

0.03167 

0.000638 

0.000707 

0.000707 

0.000708 

0.000005 

0.000000 

Major 

 

0.01882 

-0.0201 

0.002300 

0.002092 

0.002092 

0.002013 

-0.000004 

0.000002 

Any 

05 Cardiac Catheterization For 
Ischemic Heart Disease 

-0.06392 

0.02368 

0.003755 

0.004554 

0.004554 

0.004568 

-0.000051 

0.000000 

Minor 

 

0.01755 

-0.02829 

0.000951 

0.001158 

0.001158 

0.001238 

0.000004 

-0.000002 

Mod 

 

0.0356 

-0.00209 

0.001962 

0.002285 

0.002285 

0.002201 

0.000012 

0.000000 

Major 

 

-0.00279 

-0.01707 

0.000772 

0.001018 

0.001018 

0.001034 

-0.000001 

0.000000 

Any 

05 Acute & Subacute Endocarditis 

-0.02502 

0.01749 

0.000412 

0.000305 

0.000305 

0.000288 

0.000003 

0.000000 

Mod 

 

-0.08975 

-0.07522 

0.000144 

0.000075 

0.000075 

0.000068 

0.000006 

0.000001 

Major 

 

0.01372 

-0.08047 

0.000191 

0.000135 

0.000135 

0.000143 

-0.000001 

-0.000001 

Any 

05 Heart Failure 

-0.05508 

0.00951 

0.060932 

0.049014 

0.049014 

0.045716 

0.000656 

-0.000031 

Minor 

 

-0.02686 

-0.0634 

0.008470 

0.004699 

0.004699 

0.003638 

0.000101 

0.000067 

Mod 

 

-0.00863 

-0.02146 

0.037780 

0.027416 

0.027416 

0.024293 

0.000089 

0.000067 



2008 
Mean 


Appendix Table 1 

Regression Coefficients and Mean Values Used for Calculation of Real and Nominal Case-Mix Changes: 2000-2008 

 

 

Coefficients 

Means 

Real Case-Mix Change 
(2007) 

APR 
DRG 
Sev 

Level 

Variable 

IPS Period 

2008 

IPS 
Mean 

2007 
Mean 

(IPS Model) 

2007 
Mean 

(2008 model) 

Based on 
IPS 
coefficients 

Based on 
2008 
coefficients 

Major 

 

0.01093 

-0.02566 

0.013234 

0.015005 

0.015005 

0.015618 

0.000019 

-0.000016 

Any 

05 Cardiac Arrest 

-0.02919 

0.10904 

0.000093 

0.000083 

0.000083 

0.000083 

0.000000 

0.000000 

Any 

05 Peripheral & Other Vascular 
Disorders 

0.0785 

0.03289 

0.013849 

0.011744 

0.011744 

0.011706 

-0.000165 

-0.000001 

Minor 

 

-0.11006 

-0.07818 

0.003050 

0.002433 

0.002433 

0.002315 

0.000068 

0.000009 

Mod 

 

-0.05834 

-0.01699 

0.007437 

0.005784 

0.005784 

0.005458 

0.000096 

0.000006 

Major 

 

-0.04389 

-0.01763 

0.003200 

0.003187 

0.003187 

0.003591 

0.000001 

-0.000007 

Any 

05 Angina Pectoris & Coronary 
Atherosclerosis 

-0.01396 

0.08566 

0.012576 

0.009733 

0.009733 

0.009025 

0.000040 

-0.000061 

Minor 

 

-0.01233 

-0.10347 

0.003181 

0.002382 

0.002382 

0.002120 

0.000010 

0.000027 

Mod 

 

-0.01551 

-0.07584 

0.007188 

0.005297 

0.005297 

0.004905 

0.000029 

0.000030 

Major 

 

-0.02624 

-0.08006 

0.002138 

0.001916 

0.001916 

0.001896 

0.000006 

0.000002 

Any 

05 Hypertension 

-0.24351 

-0.25557 

0.002431 

0.003473 

0.003473 

0.003294 

-0.000254 

0.000046 

Minor 

 

0.16794 

0.22842 

0.000833 

0.000997 

0.000997 

0.000929 

0.000028 

-0.000015 

Mod 

 

0.22529 

0.23572 

0.001273 

0.001945 

0.001945 

0.001758 

0.000151 

-0.000044 

Major 

 

0.13723 

0.29125 

0.000316 

0.000503 

0.000503 

0.000571 

0.000026 

0.000020 

Any 

05 Cardiac Structural & Valvular 
Disorders 

0.04773 

-0.02564 

0.000485 

0.000474 

0.000474 

0.000525 

-0.000001 

-0.000001 

Mod 

 

-0.06702 

0.02208 

0.000274 

0.000245 

0.000245 

0.000253 

0.000002 

0.000000 

Major 

 

-0.00761 

-3.368E-05 

0.000131 

0.000169 

0.000169 

0.000197 

0.000000 

0.000000 

Any 

05 Cardiac Arrhythmia & Conduction 
Disorders 

-0.00984 

-0.02482 

0.015250 

0.015946 

0.015946 

0.016833 

-0.000007 

-0.000022 

Minor 

 

-0.02638 

-0.00492 

0.002600 

0.002369 

0.002369 

0.002371 

0.000006 

0.000000 

Mod 

 

-0.01703 

0.00701 

0.008582 

0.008087 

0.008087 

0.008125 

0.000008 

0.000000 



2008 
Mean 


Appendix Table 1 

Regression Coefficients and Mean Values Used for Calculation of Real and Nominal Case-Mix Changes: 2000-2008 

 

 

Coefficients 

Means 

Real Case-Mix Change 
(2007) 

APR 
DRG 
Sev 

Level 

Variable 

IPS Period 

2008 

IPS 
Mean 

2007 
Mean 

(IPS Model) 

2007 
Mean 

(2008 model) 

Based on 
IPS 
coefficients 

Based on 
2008 
coefficients 

Major 

 

-0.01521 

0.01281 

0.003768 

0.004934 

0.004934 

0.005668 

-0.000018 

0.000009 

Any 

05 Chest Pain 

-0.049 

-0.116 

0.004623 

0.006653 

0.006653 

0.006281 

-0.000099 

0.000043 

Minor 

 

0.07393 

0.14561 

0.001691 

0.001937 

0.001937 

0.001885 

0.000018 

-0.000007 

Mod 

 

0.07075 

0.17112 

0.002370 

0.003596 

0.003596 

0.003387 

0.000087 

-0.000036 

Major 

 

0.10473 

0.16565 

0.000546 

0.001041 

0.001041 

0.000949 

0.000052 

-0.000015 

Any 

05 Syncope & Collapse 

-0.06111 

0.01048 

0.009992 

0.013022 

0.013022 

0.013603 

-0.000185 

0.000006 

Minor 

 

0.07699 

0.04914 

0.002045 

0.002050 

0.002050 

0.002158 

0.000000 

0.000005 

Mod 

 

0.11569 

0.07915 

0.006336 

0.007953 

0.007953 

0.008242 

0.000187 

0.000023 

Major 

 

0.11948 

0.06111 

0.001582 

0.002908 

0.002908 

0.003037 

0.000158 

0.000008 

Any 

05 Cardiomyopathy 

-0.15218 

-0.1784 

0.000399 

0.000159 

0.000159 

0.000154 

0.000036 

0.000001 

Mod 

 

0.04063 

0.10984 

0.000207 

0.000084 

0.000084 

0.000050 

-0.000005 

-0.000004 

Major 

 

0.05236 

0.07645 

0.000137 

0.000055 

0.000055 

0.000080 

-0.000004 

0.000002 

Any 

05 
Malfunction,Reaction,Complication Of 
Cardiac/Vasc Device Or Procedure 

-0.08752 

-0.03569 

0.001461 

0.002083 

0.002083 

0.002160 

-0.000054 

-0.000003 

Mod 

 

-0.01012 

-0.02484 

0.000651 

0.000580 

0.000580 

0.000533 

0.000001 

0.000001 

Major 

 

0.07412 

0.01591 

0.000555 

0.000909 

0.000909 

0.000927 

0.000026 

0.000000 

Extreme 

 

0.05034 

0.10178 

0.000188 

0.000535 

0.000535 

0.000654 

0.000017 

0.000012 

Any 

05 Other Circulatory System 
Diagnoses 

-0.10684 

-0.01194 

0.002638 

0.003653 

0.003653 

0.003969 

-0.000108 

-0.000004 

Minor 

 

0.11816 

0.13046 

0.001094 

0.001258 

0.001258 

0.001390 

0.000019 

0.000017 

Mod 

 

0.09652 

0.06562 

0.000967 

0.001406 

0.001406 

0.001520 

0.000042 

0.000007 

Major 

 

0.04267 

-0.05312 

0.000504 

0.000723 

0.000723 

0.000739 

0.000009 

-0.000001 



2008 
Mean 


Appendix Table 1 

Regression Coefficients and Mean Values Used for Calculation of Real and Nominal Case-Mix Changes: 2000-2008 

 

 

Coefficients 

Means 

Real Case-Mix Change 
(2007) 

APR 
DRG 
Sev 

Level 

Variable 

IPS Period 

2008 

IPS 
Mean 

2007 
Mean 

(IPS Model) 

2007 
Mean 

(2008 model) 

Based on 
IPS 
coefficients 

Based on 
2008 
coefficients 

Any 

06 Major Stomach, Esophageal & 
Duodenal Procedures 

0.04306 

-0.03016 

0.002533 

0.002007 

0.002007 

0.002038 

-0.000023 

-0.000001 

Minor 

 

-0.05649 

-0.08112 

0.000341 

0.000336 

0.000336 

0.000306 

0.000000 

0.000002 

Mod 

 

-0.03838 

-0.08532 

0.000833 

0.000556 

0.000556 

0.000543 

0.000011 

0.000001 

Major 

 

-0.06662 

-0.11291 

0.001024 

0.000700 

0.000700 

0.000682 

0.000022 

0.000002 

Any 

06 Major Small & Large Bowel 
Procedures 

0.00099355 

-0.04203 

0.016258 

0.013448 

0.013448 

0.012477 

-0.000003 

0.000041 

Minor 

 

-0.05773 

-0.08278 

0.001669 

0.001396 

0.001396 

0.001383 

0.000016 

0.000001 

Mod 

 

-0.04508 

-0.08822 

0.007402 

0.005131 

0.005131 

0.004548 

0.000102 

0.000051 

Major 

 

-0.02596 

-0.05756 

0.005701 

0.004764 

0.004764 

0.004333 

0.000024 

0.000025 

Any 

06 Other Stomach, Esophageal & 
Duodenal Procedures 

0.06063 

-0.09058 

0.000195 

0.000155 

0.000155 

0.000167 

-0.000002 

-0.000001 

Mod 

 

-0.0383 

0.10094 

0.000093 

0.000061 

0.000061 

0.000063 

0.000001 

0.000000 

Any 

06 Other Small & Large Bowel 
Procedures 

0.21663 

-0.05934 

0.001576 

0.001439 

0.001439 

0.001451 

-0.000030 

-0.000001 

Minor 

 

-0.22343 

-0.09434 

0.000472 

0.000347 

0.000347 

0.000325 

0.000028 

0.000002 

Mod 

 

-0.22418 

-0.05994 

0.000609 

0.000533 

0.000533 

0.000497 

0.000017 

0.000002 

Major 

 

-0.26116 

-0.02033 

0.000415 

0.000405 

0.000405 

0.000418 

0.000003 

0.000000 

Any 

06 Peritoneal Adhesiolysis 

0.07064 

0.01761 

0.001078 

0.001006 

0.001006 

0.000957 

-0.000005 

-0.000001 

Minor 

 

-0.14474 

-0.13275 

0.000163 

0.000103 

0.000103 

0.000086 

0.000009 

0.000002 

Mod 

 

-0.05491 

-0.02247 

0.000482 

0.000392 

0.000392 

0.000358 

0.000005 

0.000001 

Major 

 

-0.04942 

-0.02212 

0.000338 

0.000338 

0.000338 

0.000308 

0.000000 

0.000001 

Any 

06 Appendectomy 

-0.18154 

-0.12576 

0.000852 

0.000784 

0.000784 

0.000830 

0.000012 

-0.000006 

Mod 

 

0.10027 

0.04441 

0.000485 

0.000376 

0.000376 

0.000391 

-0.000011 

0.000001 



2008 
Mean 


0.000000 

Extreme 

 

0.11276 

0.00472 

0.000099 

0.000079 

0.000079 

0.000136 

-0.000002 

0.000000 

Any 

06 Digestive Malignancy 

-0.03302 

-0.08379 

0.001458 

0.001024 

0.001024 

0.000877 

0.000014 

0.000012 

Minor 

 

-0.00736 

-0.02412 

0.000083 

0.000040 

0.000040 

0.000028 

0.000000 

0.000000 

Mod 

 

-0.04158 

0.00918 

0.000565 

0.000372 

0.000372 

0.000307 

0.000008 

-0.000001 

Major 

 

-0.03737 

0.00715 

0.000740 

0.000531 

0.000531 

0.000458 

0.000008 

-0.000001 

Appendix Table 1 

Regression Coefficients and Mean Values Used for Calculation of Real and Nominal Case-Mix Changes: 2000-2008 

 

 

Means 

Real Case-Mix Change 
(2007) 

APR 
DRG 
Sev 

Level 

Variable 

IPS Period 

2008 

IPS 
Mean 

2007 
Mean 

2007 
Mean 

(2008 model) 

2008 
Mean 

Based on 
IPS 
coefficients 

Based on 
2008 
coefficients 

Major 

 

0.09473 

0.07582 

0.000262 

0.000256 

0.000256 

0.000000 

0.000000 

Any 

06 Anal Procedures 

0.05519 

0.0338 

0.000747 

0.000648 

0.000648 

-0.000005 

-0.000001 

Minor 

 

-0.09461 

-0.16957 

0.000345 

0.000229 

0.000229 

0.000011 

0.000003 

Mod 

 

-0.03848 

-0.06678 

0.000319 

0.000296 

0.000296 

0.000001 

0.000001 

Any 

06 Hernia Procedures Except 
Inguinal, Femoral & Umbilical 

0.08383 

0.03802 

0.001908 

0.002062 

0.002062 

0.000013 

0.000007 

Minor 

 

-0.11543 

-0.18466 

0.000644 

0.000574 

0.000574 

0.000008 

-0.000008 

Mod 

 

-0.12688 

-0.11647 

0.000951 

0.000993 

0.000993 

-0.000005 

-0.000005 

Major 

 

-0.12692 

-0.12977 

0.000265 

0.000397 

0.000397 

-0.000017 

-0.000009 

Any 

06 Inguinal, Femoral & Umbilical 
Hernia Procedures 

0.07441 

0.05283 

0.001219 

0.001201 

0.001201 

-0.000001 

-0.000002 

Minor 

 

-0.0742 

-0.05474 

0.000370 

0.000276 

0.000276 

0.000007 

0.000000 

Mod 

 

-0.06345 

-0.08364 

0.000600 

0.000636 

0.000636 

-0.000002 

0.000000 

Major 

 

-0.11495 

-0.19404 

0.000217 

0.000240 

0.000240 

-0.000003 

0.000002 

Any 

06 Other Digestive System & 
Abdominal Procedures 

-0.14787 

-0.05856 

0.000775 

0.000652 

0.000652 

0.000018 

-0.000001 

Mod 

 

0.15197 

-0.03392 

0.000284 

0.000256 

0.000256 

-0.000004 

0.000001 

Major 

 

0.12871 

0.04082 

0.000332 

0.000253 

0.000253 

-0.000010 



Coefficients 

(IPS Model) 

0.000251 

0.000623 

0.000210 

0.000284 

0.002256 

0.000619 

0.001040 

0.000470 

0.001173 

0.000270 

0.000630 

0.000230 

0.000664 

0.000221 

0.000242 


Appendix Table 1 

Regression Coefficients and Mean Values Used for Calculation of Real and Nominal Case-Mix Changes: 2000-2008 

 

 

Means 

Real Case-Mix Change 
(2007) 

APR 
DRG 
Sev 

Level 

Variable 

IPS Period 

2008 

IPS 
Mean 

2007 
Mean 

2007 
Mean 

(2008 model) 

2008 
Mean 

Based on 
IPS 
coefficients 

Based on 
2008 
coefficients 

Any 

06 Peptic Ulcer & Gastritis 

-0.00749 

0.02473 

0.008997 

0.007860 

0.007860 

0.006846 

0.000009 

-0.000025 

Minor 

 

0.05229 

-0.02532 

0.001072 

0.000846 

0.000846 

0.000727 

-0.000012 

0.000003 

Mod 

 

0.02801 

0.02151 

0.004798 

0.003792 

0.003792 

0.003089 

-0.000028 

-0.000015 

Major 

 

0.07065 

0.02067 

0.002929 

0.002866 

0.002866 

0.002652 

-0.000004 

-0.000004 

Any 

06 Major Esophageal Disorders 

0.13683 

-0.11277 

0.000568 

0.000662 

0.000662 

0.000597 

0.000013 

0.000007 

Mod 

 

-0.02379 

0.11255 

0.000271 

0.000264 

0.000264 

0.000259 

0.000000 

-0.000001 

Major 

 

-0.07716 

0.21107 

0.000246 

0.000315 

0.000315 

0.000262 

-0.000005 

-0.000011 

Any 

06 Other Esophageal Disorders 

0.02921 

-0.004 

0.002811 

0.002750 

0.002750 

0.002643 

-0.000002 

0.000000 

Minor 

 

-0.02482 

0.00705 

0.000418 

0.000364 

0.000364 

0.000298 

0.000001 

0.000000 

Mod 

 

-0.00791 

0.07825 

0.001633 

0.001539 

0.001539 

0.001435 

0.000001 

-0.000008 

Major 

 

0.04485 

0.07501 

0.000699 

0.000786 

0.000786 

0.000811 

0.000004 

0.000002 

Any 

06 Diverticulitis & Diverticulosis 

0.01658 

0.03303 

0.006074 

0.006672 

0.006672 

0.006171 

0.000010 

-0.000017 

Minor 

 

0.01719 

0.0487 

0.000747 

0.000948 

0.000948 

0.000839 

0.000003 

-0.000005 

Mod 

 

-0.00773 

0.02398 

0.003870 

0.003699 

0.003699 

0.003370 

0.000001 

-0.000008 

Major 

 

0.00068285 

0.02573 

0.001378 

0.001894 

0.001894 

0.001787 

0.000000 

-0.000003 

Any 

06 Inflammatory Bowel Disease 

-0.02266 

-0.01474 

0.000632 

0.000563 

0.000563 

0.000586 

0.000002 

0.000000 

Mod 

 

0.03538 

0.09028 

0.000338 

0.000244 

0.000244 

0.000242 

-0.000003 

0.000000 

Major 

 

0.01053 

0.06507 

0.000211 

0.000229 

0.000229 

0.000240 

0.000000 

0.000001 

Any 

06 Gastrointestinal Vascular 
Insufficiency 

0.0203 

0.09431 

0.000887 

0.001190 

0.001190 

0.001389 

0.000006 

0.000019 

Minor 

 

-0.09681 

0.05677 

0.000080 

0.000102 

0.000102 

0.000140 

-0.000002 

0.000002 

Mod 

 

-0.03003 

-0.02889 

0.000498 

0.000596 

0.000596 

0.000666 

-0.000003 

-0.000002 



Coefficients 

(IPS Model) 


Appendix Table 1 

Regression Coefficients and Mean Values Used for Calculation of Real and Nominal Case-Mix Changes: 2000-2008 

 

 

Means 

Real Case-Mix Change 
(2007) 

APR 
DRG 
Sev 

Level 

Variable 

IPS Period 

2008 

IPS 
Mean 

2007 
Mean 

2007 
Mean 

(2008 model) 

2008 
Mean 

Based on 
IPS 
coefficients 

Based on 
2008 
coefficients 

Major 

 

0.09183 

0.06854 

0.000255 

0.000434 

0.000434 

0.000494 

0.000016 

0.000004 

Any 

06 Intestinal Obstruction 

0.06595 

0.12666 

0.007105 

0.006220 

0.006220 

0.006427 

-0.000058 

0.000026 

Minor 

 

-0.02548 

-0.09298 

0.000622 

0.000663 

0.000663 

0.000632 

-0.000001 

0.000003 

Mod 

 

0.00574 

-0.06189 

0.004262 

0.003310 

0.003310 

0.003354 

-0.000005 

-0.000003 

Major 

 

0.02802 

-0.05645 

0.002032 

0.001997 

0.001997 

0.002164 

-0.000001 

-0.000009 

Any 

06 Major Gastrointestinal & 
Peritoneal Infections 

0.06627 

0.09752 

0.002246 

0.004324 

0.004324 

0.004736 

0.000138 

0.000040 

Minor 

 

-0.09516 

0.01566 

0.000121 

0.000120 

0.000120 

0.000156 

0.000000 

0.000001 

Mod 

 

-0.01698 

-0.02835 

0.000999 

0.001724 

0.001724 

0.001632 

-0.000012 

0.000003 

Major 

 

-0.00869 

-0.0008119 

0.001066 

0.002073 

0.002073 

0.002438 

-0.000009 

0.000000 

Any 

06 Non-Bacterial Gastroenteritis, 
Nausea & Vomiting 

0.10293 

-0.03172 

0.007347 

0.009905 

0.009905 

0.009019 

0.000263 

0.000028 

Minor 

 

-0.03836 

0.12072 

0.000495 

0.000692 

0.000692 

0.000693 

-0.000008 

0.000000 

Mod 

 

-0.06835 

0.11482 

0.004910 

0.006090 

0.006090 

0.005342 

-0.000081 

-0.000086 

Major 

 

-0.0217 

0.07638 

0.001870 

0.002960 

0.002960 

0.002792 

-0.000024 

-0.000013 

Any 

06 Abdominal Pain 

0.15094 

-0.04846 

0.002122 

0.002577 

0.002577 

0.002268 

0.000069 

0.000015 

Minor 

 

-0.08509 

0.09649 

0.000370 

0.000409 

0.000409 

0.000376 

-0.000003 

-0.000003 

Mod 

 

-0.13037 

0.08563 

0.001356 

0.001499 

0.001499 

0.001246 

-0.000019 

-0.000022 

Major 

 

-0.17154 

0.11838 

0.000376 

0.000623 

0.000623 

0.000595 

-0.000042 

-0.000003 

Any 

06 Malfunction, Reaction & 
Complication Of Gi Device Or 
Procedure 

0.04451 

0.00964 

0.001378 

0.001374 

0.001374 

0.001218 

0.000000 

-0.000002 

Minor 

 

0.00010214 

0.16661 

0.000121 

0.000085 

0.000085 

0.000074 

0.000000 

-0.000002 

Mod 

 

0.14598 

0.07603 

0.000692 

0.000624 

0.000624 

0.000531 

-0.000010 

-0.000007 



Coefficients 

(IPS Model) 


Appendix Table 1 

Regression Coefficients and Mean Values Used for Calculation of Real and Nominal Case-Mix Changes: 2000-2008 

 

 

Means 

Real Case-Mix Change 
(2007) 

APR 
DRG 
Sev 

Level 

Variable 

IPS Period 

2008 

IPS 
Mean 

2007 
Mean 

2007 
Mean 

(2008 model) 

2008 
Mean 

Based on 
IPS 
coefficients 

Based on 
2008 
coefficients 

Major 

 

0.11109 

0.00399 

0.000510 

0.000569 

0.000569 

0.000500 

0.000007 

0.000000 

Any 

06 Other & Unspecified 
Gastrointestinal Hemorrhage 

-0.07484 

0.06689 

0.006342 

0.006540 

0.006540 

0.006705 

-0.000015 

0.000011 

Minor 

 

0.06936 

-0.03296 

0.000683 

0.000599 

0.000599 

0.000645 

-0.000006 

-0.000002 

Mod 

 

0.1206 

-0.00944 

0.003474 

0.003096 

0.003096 

0.003064 

-0.000046 

0.000000 

Major 

 

0.11956 

-0.0133 

0.002051 

0.002466 

0.002466 

0.002598 

0.000050 

-0.000002 

Any 

06 Other Digestive System 
Diagnoses 

0.03811 

0.03223 

0.006703 

0.007475 

0.007475 

0.007491 

0.000029 

0.000001 

Minor 

 

0.02866 

0.04259 

0.002061 

0.002111 

0.002111 

0.002150 

0.000001 

0.000002 

Mod 

 

0.00595 

0.03783 

0.002859 

0.002893 

0.002893 

0.002840 

0.000000 

-0.000002 

Major 

 

0.00915 

0.01466 

0.001637 

0.002212 

0.002212 

0.002166 

0.000005 

-0.000001 

Any 

07 Major Pancreas, Liver & Shunt 
Procedures 

-0.10134 

-0.14183 

0.000833 

0.000861 

0.000861 

0.000813 

-0.000003 

0.000007 

Mod 

 

-0.05253 

0.02728 

0.000220 

0.000226 

0.000226 

0.000211 

0.000000 

0.000000 

Major 

 

0.0258 

0.03656 

0.000456 

0.000444 

0.000444 

0.000417 

0.000000 

-0.000001 

Extreme 

 

0.0109 

0.0229 

0.000124 

0.000147 

0.000147 

0.000148 

0.000000 

0.000000 

Any 

07 Major Biliary Tract Procedures 

0.11299 

0.0608 

0.000651 

0.000313 

0.000313 

0.000314 

-0.000038 

0.000000 

Mod 

 

-0.19016 

-0.22748 

0.000300 

0.000121 

0.000121 

0.000125 

0.000034 

-0.000001 

Major 

 

-0.21398 

-0.14907 

0.000230 

0.000134 

0.000134 

0.000140 

0.000020 

-0.000001 

Any 

07 Cholecystectomy Except 
Laparoscopic 

-0.03449 

0.00666 

0.002335 

0.001611 

0.001611 

0.001534 

0.000025 

-0.000001 

Minor 

 

0.02876 

-0.14356 

0.000252 

0.000157 

0.000157 

0.000167 

-0.000003 

-0.000001 

Mod 

 

0.05303 

-0.05718 

0.001133 

0.000610 

0.000610 

0.000557 

-0.000028 

0.000003 

Major 

 

0.06707 

-0.07877 

0.000740 

0.000630 

0.000630 

0.000576 

-0.000007 

0.000004 



Coefficients 

(IPS Model) 


Appendix Table 1 
0.000412 

Regression Coefficients and Mean Values Used for Calculation of Real and Nominal Case-Mix Changes: 2000-2008 
0.000412 

 
-0.000010 

 
0.000007 

Any 

07 Alcoholic Liver Disease 

0.07183 

-0.12424 

0.000558 

0.000358 

Means 
Mod 

Real Case-Mix Change 
(2007) 


APR 
DRG 
Sev 
0.2297 

Level 
0.000160 

Variable 
0.000110 

IPS Period 
0.000110 

2008 
0.000070 

IPS 
Mean 
0.000012 

2007 
Mean 
-0.000009 

-0.23564 

2007 
Mean 
Major 

(2008 model) 


2008 
Mean 
-0.15066 

Based on 
IPS 
coefficients 
0.09965 

Based on 
2008 
coefficients 
0.000351 

0.000244 

0.000244 

0.000237 

0.000016 

-0.000001 

Any 

07 Laparoscopic Cholecystectomy 

0.0818 

-0.04657 

0.003876 

0.004876 

0.004876 

0.004934 

0.000082 

-0.000003 

Minor 

 

-0.02245 

-0.00604 

0.000584 

0.000644 

0.000644 

0.000617 

-0.000001 

0.000000 

Mod 

 

0.01586 

0.06599 

0.001739 

0.002117 

0.002117 

0.002154 

0.000006 

0.000002 

Major 

 

-0.07994 

0.04225 

0.001337 

0.001812 

0.001812 

0.001817 

-0.000038 

0.000000 

Any 

07 Other Hepatobiliary, Pancreas & 
Abdominal Procedures 

-0.18022 

-0.04368 

0.000367 

0.000267 

0.000267 

0.000221 

0.000018 

0.000002 

Mod 

 

0.08562 

-0.09142 

0.000080 

0.000059 

0.000059 

0.000052 

-0.000002 

0.000001 

Major 

 

0.09663 

0.01604 

0.000185 

0.000121 

0.000121 

0.000103 

-0.000006 

0.000000 

Any 

07 Hepatic Coma & Other Major 
Acute Liver Disorders 

0.01574 

0.11567 

0.000731 

0.000988 

0.000988 

0.001003 

0.000004 

0.000002 

Mod 

 

-0.05263 

-0.14068 

0.000341 

0.000375 

0.000375 

0.000410 

-0.000002 

-0.000005 

Major 

 

-0.12555 

-0.13083 

0.000335 

0.000478 

0.000478 

0.000485 

-0.000018 

-0.000001 

Any 

07 Malignancy Of Hepatobiliary 
System & Pancreas 

-0.1041 

-0.22743 

0.001110 

0.000710 

0.000710 

0.000643 

0.000042 

0.000015 

Mod 

 

-0.03612 

0.16239 

0.000520 

0.000256 

0.000256 

0.000236 

0.000010 

-0.000003 

Major 

 

-0.00253 

0.14 

0.000466 

0.000361 

0.000361 

0.000339 

0.000000 

-0.000003 

Any 

07 Disorders Of Pancreas Except 
Malignancy 

-0.00683 

-0.09187 

0.002319 

0.002821 

0.002821 

0.002774 

-0.000003 

0.000004 

Minor 

 

-0.04211 

0.01244 

0.000271 

0.000298 

0.000298 

0.000283 

-0.000001 

0.000000 

Mod 

 

-0.0251 

0.12151 

0.001314 

0.001349 

0.001349 

0.001289 

-0.000001 

-0.000007 

Major 

 

0.02589 

0.10079 

0.000648 

0.000971 

0.000971 

0.000983 

0.000008 

0.000001 



Coefficients 

(IPS Model) 


Appendix Table 1 

Regression Coefficients and Mean Values Used for Calculation of Real and Nominal Case-Mix Changes: 2000-2008 

 

 

Means 

Real Case-Mix Change 
(2007) 

APR 
DRG 
Sev 

Level 

Variable 

IPS Period 

2008 

IPS 
Mean 

2007 
Mean 

2007 
Mean 

(2008 model) 

2008 
Mean 

Based on 
IPS 
coefficients 

Based on 
2008 
coefficients 

Any 

07 Other Disorders Of The Liver 

-0.03645 

0.04264 

0.001066 

0.001092 

0.001092 

0.001027 

-0.000001 

-0.000003 

Mod 

 

0.09027 

0.00971 

0.000303 

0.000370 

0.000370 

0.000332 

0.000006 

0.000000 

Major 

 

-0.0452 

-0.07795 

0.000600 

0.000578 

0.000578 

0.000527 

0.000001 

0.000004 

Extreme 

 

0.0673 

-0.02595 

0.000105 

0.000113 

0.000113 

0.000117 

0.000001 

0.000000 

Any 

07 Disorders Of Gallbladder & Biliary 
Tract 

-0.0599 

-0.02857 

0.002138 

0.002503 

0.002503 

0.002623 

-0.000022 

-0.000003 

Minor 

 

0.09303 

0.07321 

0.000163 

0.000232 

0.000232 

0.000203 

0.000006 

-0.000002 

Mod 

 

0.06167 

0.07322 

0.001088 

0.001209 

0.001209 

0.001220 

0.000007 

0.000001 

Major 

 

0.05988 

0.06463 

0.000778 

0.000895 

0.000895 

0.001048 

0.000007 

0.000010 

Any 

08 Hip Joint Replacement 

0.15321 

0.16291 

0.031431 

0.030015 

0.030015 

0.029154 

-0.000217 

-0.000140 

Minor 

 

0.11393 

-0.0313 

0.003478 

0.002121 

0.002121 

0.001791 

-0.000155 

0.000010 

Mod 

 

0.05304 

-0.04484 

0.016165 

0.013085 

0.013085 

0.012401 

-0.000163 

0.000031 

Major 

 

0.04714 

-0.04367 

0.011578 

0.014349 

0.014349 

0.014344 

0.000131 

0.000000 

Any 

08 Knee Joint Replacement 

0.21463 

0.11908 

0.027612 

0.038163 

0.038163 

0.038030 

0.002265 

-0.000016 

Minor 

 

0.02531 

0.02458 

0.013923 

0.016032 

0.016032 

0.014848 

0.000053 

-0.000029 

Mod 

 

0.01546 

0.03545 

0.012232 

0.019344 

0.019344 

0.020135 

0.000110 

0.000028 

Major 

 

-0.0007566 

0.03476 

0.001381 

0.002585 

0.002585 

0.002848 

-0.000001 

0.000009 

Any 

08 Dorsal & Lumbar Fusion Proc For 
Curvature Of Back 

0.19356 

0.1842 

0.000083 

0.000323 

0.000323 

0.000280 

0.000046 

-0.000008 

Any 

08 Dorsal & Lumbar Fusion Proc 
Except For Curvature Of Back 

0.17272 

0.06049 

0.002814 

0.005105 

0.005105 

0.005340 

0.000396 

0.000014 

Minor 

 

-0.01348 

-0.02088 

0.000957 

0.001354 

0.001354 

0.001458 

-0.000005 

-0.000002 

Mod 

 

0.00753 

0.0136 

0.001353 

0.002629 

0.002629 

0.002682 

0.000010 

0.000001 



Coefficients 

(IPS Model) 


Appendix Table 1 

Regression Coefficients and Mean Values Used for Calculation of Real and Nominal Case-Mix Changes: 2000-2008 

 

 

Means 

Real Case-Mix Change 
(2007) 

APR 
DRG 
Sev 

Level 

Variable 

IPS Period 

2008 

IPS 
Mean 

2007 
Mean 

2007 
Mean 

(2008 model) 

2008 
Mean 

Based on 
IPS 
coefficients 

Based on 
2008 
coefficients 

Major 

 

-0.01919 

0.07425 

0.000475 

0.000995 

0.000995 

0.001068 

-0.000010 

0.000005 

Any 

08 Amputation Of Lower Limb Except 
Toes 

0.24443 

0.13598 

0.007376 

0.004241 

0.004241 

0.003703 

-0.000766 

-0.000073 

Minor 

 

-0.01916 

-0.01087 

0.000648 

0.000290 

0.000290 

0.000205 

0.000007 

0.000001 

Mod 

 

0.00998 

0.0163 

0.003522 

0.001533 

0.001533 

0.001228 

-0.000020 

-0.000005 

Major 

 

-0.00557 

0.02588 

0.002817 

0.001898 

0.001898 

0.001685 

0.000005 

-0.000006 

Any 

08 Hip & Femur Procedures For 
Trauma Except Joint Replacement 

0.23189 

0.27007 

0.024135 

0.019863 

0.019863 

0.019441 

-0.000991 

-0.000114 

Minor 

 

0.07959 

-0.10083 

0.005599 

0.003012 

0.003012 

0.002767 

-0.000206 

0.000025 

Mod 

 

0.06575 

-0.08916 

0.013562 

0.010984 

0.010984 

0.010636 

-0.000170 

0.000031 

Major 

 

0.05825 

-0.07232 

0.004632 

0.005301 

0.005301 

0.005396 

0.000039 

-0.000007 

Any 

08 Hip & Femur Procedures For Non-
Trauma Except Joint Replacement 

0.44508 

0.12425 

0.001771 

0.001948 

0.001948 

0.001905 

0.000079 

-0.000005 

Minor 

 

-0.24277 

0.08647 

0.000281 

0.000325 

0.000325 

0.000292 

-0.000011 

-0.000003 

Mod 

 

-0.22936 

0.0026 

0.001059 

0.001032 

0.001032 

0.001069 

0.000006 

0.000000 

Major 

 

-0.18734 

-0.06624 

0.000415 

0.000514 

0.000514 

0.000500 

-0.000019 

0.000001 

Any 

08 Intervertebral Disc Excision & 
Decompression 

0.38265 

0.13465 

0.004680 

0.007785 

0.007785 

0.007710 

0.001188 

-0.000010 

Minor 

 

-0.24059 

-0.13986 

0.001819 

0.001332 

0.001332 

0.001310 

0.000117 

0.000003 

Mod 

 

-0.17169 

-0.06834 

0.002367 

0.003053 

0.003053 

0.002986 

-0.000118 

0.000005 

Major 

 

-0.20536 

-0.01744 

0.000475 

0.003284 

0.003284 

0.003302 

-0.000577 

0.000000 

Any 

08 Skin Graft, Except Hand, For 
Musculoskeletal & Connective Tissue 
Diagnoses 

0.19985 

-0.16058 

0.000424 

0.000327 

0.000327 

0.000313 

-0.000019 

0.000002 



Coefficients 

(IPS Model) 


Appendix Table 1 

Regression Coefficients and Mean Values Used for Calculation of Real and Nominal Case-Mix Changes: 2000-2008 

 

 

Means 

Real Case-Mix Change 
(2007) 

APR 
DRG 
Sev 

Level 

Variable 

IPS Period 

2008 

IPS 
Mean 

2007 
Mean 

2007 
Mean 

(2008 model) 

2008 
Mean 

Based on 
IPS 
coefficients 

Based on 
2008 
coefficients 

Mod 

 

-0.19157 

0.12526 

0.000169 

0.000133 

0.000133 

0.000142 

0.000007 

0.000001 

Major 

 

0.01348 

0.11422 

0.000166 

0.000135 

0.000135 

0.000107 

0.000000 

-0.000003 

Any 

08 Knee & Lower Leg Procedures 
Except Foot 

0.31507 

0.15488 

0.006078 

0.006461 

0.006461 

0.006409 

0.000121 

-0.000008 

Minor 

 

-0.0498 

-0.0226 

0.002358 

0.001897 

0.001897 

0.001939 

0.000023 

-0.000001 

Mod 

 

-0.0896 

0.01838 

0.002942 

0.003410 

0.003410 

0.003247 

-0.000042 

-0.000003 

Major 

 

-0.12229 

-0.01239 

0.000667 

0.001015 

0.001015 

0.001057 

-0.000043 

-0.000001 

Any 

08 Foot & Toe Procedures 

0.07147 

-0.13353 

0.003860 

0.003475 

0.003475 

0.003242 

-0.000028 

0.000031 

Minor 

 

0.15238 

0.08601 

0.000396 

0.000207 

0.000207 

0.000222 

-0.000029 

0.000001 

Mod 

 

-0.01654 

0.11304 

0.001767 

0.001388 

0.001388 

0.001207 

0.000006 

-0.000020 

Major 

 

-0.05818 

0.03682 

0.001560 

0.001621 

0.001621 

0.001524 

-0.000004 

-0.000004 

Any 

08 Shoulder, Upper Arm & Forearm 
Procedures 

0.45981 

0.26365 

0.005440 

0.006557 

0.006557 

0.006458 

0.000514 

-0.000026 

Minor 

 

-0.18825 

-0.02116 

0.001551 

0.001105 

0.001105 

0.001049 

0.000084 

0.000001 

Mod 

 

-0.11975 

0.04978 

0.003554 

0.004646 

0.004646 

0.004472 

-0.000131 

-0.000009 

Major 

 

-0.15573 

-0.00937 

0.000316 

0.000758 

0.000758 

0.000854 

-0.000069 

-0.000001 

Any 

08 Hand & Wrist Procedures 

0.18267 

-0.01829 

0.000434 

0.000296 

0.000296 

0.000283 

-0.000025 

0.000000 

Mod 

 

-0.08046 

0.09427 

0.000319 

0.000130 

0.000130 

0.000127 

0.000015 

0.000000 

Any 

08 Tendon, Muscle & Other Soft 
Tissue Procedures 

-0.01123 

0.04951 

0.001525 

0.001490 

0.001490 

0.001509 

0.000000 

0.000001 

Minor 

 

0.16238 

0.05399 

0.000549 

0.000407 

0.000407 

0.000385 

-0.000023 

-0.000001 

Mod 

 

0.10922 

-0.02546 

0.000651 

0.000611 

0.000611 

0.000620 

-0.000004 

0.000000 

Major 

 

0.09909 

-0.13713 

0.000287 

0.000414 

0.000414 

0.000419 

0.000013 

-0.000001 



Coefficients 

(IPS Model) 


Appendix Table 1 

Regression Coefficients and Mean Values Used for Calculation of Real and Nominal Case-Mix Changes: 2000-2008 

 

 

Means 

Real Case-Mix Change 
(2007) 

APR 
DRG 
Sev 

Level 

Variable 

IPS Period 

2008 

IPS 
Mean 

2007 
Mean 

2007 
Mean 

(2008 model) 

2008 
Mean 

Based on 
IPS 
coefficients 

Based on 
2008 
coefficients 

Any 

08 Other Musculoskeletal System & 
Connective Tissue Procedures 

0.39482 

0.20437 

0.001142 

0.001310 

0.001310 

0.001351 

0.000066 

0.000008 

Minor 

 

-0.19471 

-0.1934 

0.000179 

0.000156 

0.000156 

0.000166 

0.000004 

-0.000002 

Mod 

 

-0.23752 

-0.14681 

0.000715 

0.000724 

0.000724 

0.000771 

-0.000002 

-0.000007 

Major 

 

-0.19551 

-0.18666 

0.000214 

0.000383 

0.000383 

0.000344 

-0.000033 

0.000007 

Any 

08 Cervical Spinal Fusion & Other 
Back/Neck Proc Exc Disc Excis/ 
Decomp 

-0.01311 

0.39694 

0.001777 

0.002426 

0.002426 

0.002497 

-0.000009 

0.000028 

Minor 

 

0.18949 

-0.2867 

0.000667 

0.000813 

0.000813 

0.000834 

0.000028 

-0.000006 

Mod 

 

0.1797 

-0.24617 

0.000865 

0.001160 

0.001160 

0.001210 

0.000053 

-0.000012 

Major 

 

0.23674 

-0.17909 

0.000233 

0.000371 

0.000371 

0.000356 

0.000033 

0.000003 

Any 

08 Fracture Of Femur 

0.19997 

0.24176 

0.002221 

0.001571 

0.001571 

0.001383 

-0.000130 

-0.000045 

Minor 

 

0.12867 

-0.07738 

0.000558 

0.000278 

0.000278 

0.000240 

-0.000036 

0.000003 

Mod 

 

0.06793 

-0.13788 

0.001161 

0.000890 

0.000890 

0.000768 

-0.000018 

0.000017 

Major 

 

-0.02382 

-0.0015 

0.000479 

0.000383 

0.000383 

0.000346 

0.000002 

0.000000 

Any 

08 Fracture Of Pelvis Or Dislocation 
Of Hip 

0.24225 

0.39101 

0.004400 

0.004466 

0.004466 

0.004472 

0.000016 

0.000002 

Minor 

 

-0.08598 

-0.26924 

0.001171 

0.000811 

0.000811 

0.000818 

0.000031 

-0.000002 

Mod 

 

-0.07492 

-0.25288 

0.002348 

0.002395 

0.002395 

0.002352 

-0.000004 

0.000011 

Major 

 

-0.03247 

-0.21897 

0.000845 

0.001197 

0.001197 

0.001225 

-0.000011 

-0.000006 

Any 

08 Fractures & Dislocations Except 
Femur, Pelvis & Back 

0.19038 

0.45638 

0.005902 

0.005963 

0.005963 

0.005668 

0.000012 

-0.000135 

Minor 

 

0.04374 

-0.222 

0.001774 

0.001180 

0.001180 

0.001066 

-0.000026 

0.000025 

Mod 

 

0.06435 

-0.19829 

0.003359 

0.003613 

0.003613 

0.003271 

0.000016 

0.000068 



Coefficients 

(IPS Model) 


Appendix Table 1 

Regression Coefficients and Mean Values Used for Calculation of Real and Nominal Case-Mix Changes: 2000-2008 

 

 

Means 

Real Case-Mix Change 
(2007) 

APR 
DRG 
Sev 

Level 

Variable 

IPS Period 

2008 

IPS 
Mean 

2007 
Mean 

2007 
Mean 

(2008 model) 

2008 
Mean 

Based on 
IPS 
coefficients 

Based on 
2008 
coefficients 

Major 

 

0.06305 

-0.22216 

0.000731 

0.001109 

0.001109 

0.001234 

0.000024 

-0.000028 

Any 

08 Musculoskeletal Malignancy & 
Pathol Fracture D/T Muscskel Malig 

-0.12506 

-0.02979 

0.001327 

0.000751 

0.000751 

0.000701 

0.000072 

0.000001 

Minor 

 

0.12315 

-0.0918 

0.000099 

0.000042 

0.000042 

0.000048 

-0.000007 

-0.000001 

Mod 

 

0.17323 

0.14069 

0.000635 

0.000282 

0.000282 

0.000270 

-0.000061 

-0.000002 

Major 

 

0.12559 

0.07602 

0.000565 

0.000403 

0.000403 

0.000345 

-0.000020 

-0.000004 

Any 

08 Osteomyelitis, Septic Arthritis & 
Other Musculoskeletal Infections 

0.02178 

0.14037 

0.002144 

0.002141 

0.002141 

0.002252 

0.000000 

0.000016 

Minor 

 

-0.03296 

-0.20358 

0.000099 

0.000070 

0.000070 

0.000083 

0.000001 

-0.000003 

Mod 

 

0.00205 

-0.16806 

0.001053 

0.000920 

0.000920 

0.000982 

0.000000 

-0.000010 

Major 

 

0.12209 

-0.13623 

0.000912 

0.001011 

0.001011 

0.001012 

0.000012 

0.000000 

Any 

08 Connective Tissue Disorders 

-0.03587 

0.04514 

0.001688 

0.001219 

0.001219 

0.001099 

0.000017 

-0.000005 

Minor 

 

0.14218 

0.13049 

0.000507 

0.000282 

0.000282 

0.000268 

-0.000032 

-0.000002 

Mod 

 

0.15704 

0.02191 

0.000695 

0.000483 

0.000483 

0.000395 

-0.000033 

-0.000002 

Major 

 

0.07419 

-0.0009551 

0.000447 

0.000375 

0.000375 

0.000336 

-0.000005 

0.000000 

Any 

08 Other Back & Neck Disorders, 
Fractures & Injuries 

0.0041 

0.1645 

0.014331 

0.012654 

0.012654 

0.011822 

-0.000007 

-0.000137 

Minor 

 

0.17213 

-0.02941 

0.004661 

0.003880 

0.003880 

0.003217 

-0.000134 

0.000019 

Mod 

 

0.13002 

-0.01813 

0.007539 

0.006111 

0.006111 

0.005900 

-0.000186 

0.000004 

Major 

 

0.14773 

-0.01446 

0.002048 

0.002499 

0.002499 

0.002543 

0.000067 

-0.000001 

Any 

08 Malfunction, Reaction, Complic Of 
Orthopedic Device Or Procedure 

0.06958 

-0.08681 

0.001547 

0.001472 

0.001472 

0.001516 

-0.000005 

-0.000004 

Minor 

 

0.12997 

0.23302 

0.000319 

0.000216 

0.000216 

0.000217 

-0.000013 

0.000000 

Mod 

 

0.03561 

0.25164 

0.000903 

0.000786 

0.000786 

0.000810 

-0.000004 

0.000006 



Coefficients 

(IPS Model) 


Appendix Table 1 

Regression Coefficients and Mean Values Used for Calculation of Real and Nominal Case-Mix Changes: 2000-2008 

 

 

Means 

Real Case-Mix Change 
(2007) 

APR 
DRG 
Sev 

Level 

Variable 

IPS Period 

2008 

IPS 
Mean 

2007 
Mean 

2007 
Mean 

(2008 model) 

2008 
Mean 

Based on 
IPS 
coefficients 

Based on 
2008 
coefficients 

Major 

 

0.05968 

0.13923 

0.000306 

0.000404 

0.000404 

0.000415 

0.000006 

0.000002 

Any 

08 Other Musculoskeletal System & 
Connective Tissue Diagnoses 

-0.13294 

0.02863 

0.006020 

0.008061 

0.008061 

0.007922 

-0.000271 

-0.000004 

Minor 

 

0.25998 

0.07334 

0.001474 

0.001347 

0.001347 

0.001186 

-0.000033 

-0.000012 

Mod 

 

0.23918 

0.09426 

0.003493 

0.004568 

0.004568 

0.004312 

0.000257 

-0.000024 

Major 

 

0.2231 

0.07755 

0.001021 

0.001993 

0.001993 

0.002244 

0.000217 

0.000019 

Any 

09 Skin Graft For Skin & 
Subcutaneous Tissue Diagnoses 

0.44743 

-0.0251 

0.003181 

0.001659 

0.001659 

0.001610 

-0.000681 

0.000001 

Minor 

 

-0.41087 

-0.10445 

0.001113 

0.000549 

0.000549 

0.000479 

0.000232 

0.000007 

Mod 

 

-0.29901 

0.00506 

0.001420 

0.000722 

0.000722 

0.000699 

0.000209 

0.000000 

Major 

 

-0.25278 

0.0214 

0.000609 

0.000350 

0.000350 

0.000391 

0.000066 

0.000001 

Any 

09 Mastectomy Procedures 

-0.01155 

-0.03817 

0.003844 

0.002598 

0.002598 

0.002330 

0.000014 

0.000010 

Minor 

 

-0.09938 

-0.06931 

0.002469 

0.001478 

0.001478 

0.001284 

0.000099 

0.000013 

Mod 

 

-0.04776 

-0.02852 

0.001308 

0.001014 

0.001014 

0.000957 

0.000014 

0.000002 

Any 

09 Breast Procedures Except 
Mastectomy 

0.0281 

-0.06085 

0.000479 

0.000282 

0.000282 

0.000238 

-0.000006 

0.000003 

Minor 

 

-0.12284 

-0.04495 

0.000367 

0.000219 

0.000219 

0.000189 

0.000018 

0.000001 

Any 

09 Other Skin, Subcutaneous Tissue 
& Related Procedures 

0.1981 

0.00967 

0.001589 

0.001925 

0.001925 

0.001890 

0.000067 

0.000000 

Minor 

 

-0.22027 

-0.11413 

0.000249 

0.000245 

0.000245 

0.000223 

0.000001 

0.000002 

Mod 

 

-0.0652 

-0.08076 

0.000775 

0.000968 

0.000968 

0.000942 

-0.000013 

0.000002 

Major 

 

-0.01874 

-0.08921 

0.000504 

0.000598 

0.000598 

0.000622 

-0.000002 

-0.000002 

Any 

09 Skin Ulcers 

0.30134 

-0.05464 

0.007465 

0.005375 

0.005375 

0.005019 

-0.000630 

0.000019 

Minor 

 

-0.34909 

0.00257 

0.000839 

0.000355 

0.000355 

0.000270 

0.000169 

0.000000 



Coefficients 

(IPS Model) 


Appendix Table 1 

Regression Coefficients and Mean Values Used for Calculation of Real and Nominal Case-Mix Changes: 2000-2008 

 

 

Means 

Real Case-Mix Change 
(2007) 

APR 
DRG 
Sev 

Level 

Variable 

IPS Period 

2008 

IPS 
Mean 

2007 
Mean 

2007 
Mean 

(2008 model) 

2008 
Mean 

Based on 
IPS 
coefficients 

Based on 
2008 
coefficients 

-0.07736 

0.008557 

0.009412 

0.009412 

0.009536 

-0.000052 

-0.000010 

Mod 

 

-0.06071 

Major 

 

-0.06593 

0.004339 

0.005810 

0.005810 

0.005876 

-0.000044 

-0.000004 

-0.02989 

Any 

09 Contusion, Open Wound & Other 
Trauma To Skin & Subcutaneous 
Tissue 

-0.07192 

0.003165 

0.003337 

0.003337 

0.003319 

-0.000127 

0.000001 

-0.73963 

Minor 

 

0.13792 

0.000711 

0.000481 

0.000481 

0.000525 

-0.000195 

0.000006 

0.84764 

Mod 

 

0.20755 

0.001921 

0.002065 

0.002065 

0.002009 

0.000128 

-0.000012 

0.89099 

Major 

 

0.19835 

0.000530 

0.000729 

0.000729 

0.000740 

0.000172 

0.000002 

0.86233 

Any 

09 Other Skin, Subcutaneous Tissue 
& Breast Disorders 

0.21604 

0.000769 

0.000935 

0.000935 

0.000936 

0.000043 

0.000000 

0.25961 

Minor 

 

-0.31767 

0.000204 

0.000214 

0.000214 

0.000185 

-0.000004 

0.000009 

-0.36284 

Mod 

 

-0.15895 

0.000396 

0.000479 

0.000479 

0.000454 

-0.000027 

0.000004 

-0.31994 

Major 

 

-0.1989 

0.000163 

0.000214 

0.000214 

0.000267 

-0.000011 

-0.000010 

-0.21507 

Any 

10 Pituitary & Adrenal Procedures 

0.08183 

0.000105 

0.000102 

0.000102 

0.000115 

0.000000 

0.000001 

-0.01574 

Mod 

 

-0.15064 

0.09988 

0.004540 

0.003018 

0.003018 

0.002727 

0.000229 

-0.000029 

Major 

 

-0.13585 

0.08351 

0.001997 

0.001858 

0.001858 

0.001853 

0.000019 

0.000000 

Any 

09 Major Skin Disorders 

0.05339 

0.06223 

0.000660 

0.000531 

0.000531 

0.000542 

-0.000007 

0.000001 

Mod 

 

-0.05469 

0.02091 

0.000396 

0.000318 

0.000318 

0.000309 

0.000004 

0.000000 

Major 

 

-0.01052 

-0.03593 

0.000182 

0.000146 

0.000146 

0.000142 

0.000000 

0.000000 

Any 

09 Malignant Breast Disorders 

-0.14142 

-0.00552 

0.000134 

0.000142 

0.000142 

0.000128 

-0.000001 

0.000000 

Mod 

 

0.01955 

0.02386 

0.000083 

0.000046 

0.000046 

0.000055 

-0.000001 

0.000000 

Any 

09 Cellulitis & Other Bacterial Skin 
Infections 

0.05708 

0.1048 

0.015352 

0.017660 

0.017660 

0.017978 

0.000132 

0.000033 

Minor 

 

-0.0639 

-0.12468 

0.002259 

0.002063 

0.002063 

0.002178 

0.000013 

-0.000014 



Coefficients 

(IPS Model) 


10 Other Procedures For Endocrine, 
Nutritional & Metabolic Disorders 

0.26553 

-0.0013 

0.000316 

0.000283 

0.000283 

0.000307 

-0.000009 

0.000000 

Mod 

 

-0.18678 

0.03939 

0.000131 

0.000075 

0.000075 

0.000087 

0.000010 

0.000000 

Major 

 

-0.19132 

-0.01189 

0.000144 

0.000154 

0.000154 

0.000170 

-0.000002 

0.000000 

Any 

10 Diabetes 

-0.06868 

0.02045 

0.008636 

0.008643 

0.008643 

0.008482 

0.000000 

-0.000003 

Minor 

 

0.06354 

-0.02474 

0.003264 

0.002659 

0.002659 

0.002445 

-0.000038 

0.000005 

Mod 

 

0.09207 

0.01895 

0.003184 

0.003433 

0.003433 

0.003448 

0.000023 

0.000000 

Major 

 

0.08454 

-0.01939 

0.002023 

0.002247 

0.002247 

0.002261 

0.000019 

0.000000 

Any 

10 Malnutrition, Failure To Thrive & 
Other Nutritional Disorders 

0.11751 

0.23083 

0.001528 

0.001321 

0.001321 

0.001304 

-0.000024 

-0.000004 

Mod 

 

-0.1392 

-0.10453 

0.000705 

0.000589 

0.000589 

0.000590 

0.000016 

0.000000 

Major 

 

0.08468 

-0.14257 

0.000766 

0.000657 

0.000657 

0.000645 

-0.000009 

0.000002 

Any 

10 Hypovolemia & Related 
Electrolyte Disorders 

0.14646 

0.15685 

0.014041 

0.010238 

0.010238 

0.009465 

-0.000557 

-0.000121 

Minor 

 

-0.07589 

-0.17184 

0.000380 

0.000257 

0.000257 

0.000347 

0.000009 

-0.000015 

Mod 

 

-0.07628 

-0.08294 

0.008330 

0.006094 

0.006094 

0.005794 

0.000171 

0.000025 

Major 

 

-0.08228 

-0.0804 

0.005066 

0.003609 

0.003609 

0.003104 

0.000120 

0.000041 

Any 

10 Other Endocrine Disorders 

0.22535 

0.01698 

0.001892 

0.002332 

0.002332 

0.002399 

0.000099 

0.000001 

Minor 

 

-0.21165 

0.01158 

0.000447 

0.000352 

0.000352 

0.000327 

0.000020 

0.000000 

Appendix Table 1 

Regression Coefficients and Mean Values Used for Calculation of Real and Nominal Case-Mix Changes: 2000-2008 

 

 

Coefficients 

Means 

Real Case-Mix Change 
(2007) 

APR 
DRG 
Sev 

Level 

Variable 

IPS Period 

IPS 
Mean 

2007 
Mean 

(IPS Model) 

2007 
Mean 

(2008 model) 

2008 
Mean 

Based on 
IPS 
coefficients 

Based on 
2008 
coefficients 

Any 

10 Procedures For Obesity 

0.01792 

0.03187 

0.000108 

0.000297 

0.000297 

0.000003 

0.000001 

Any 

10 Thyroid, Parathyroid & 
Thyroglossal Procedures 

-0.04397 

-0.09064 

0.000319 

0.000644 

0.000644 

-0.000014 

0.000003 

Minor 

 

0.0938 

0.01113 

0.000163 

0.000302 

0.000302 

0.000013 

0.000000 

Mod 

 

0.09357 

-0.00976 

0.000118 

0.000258 

0.000258 

0.000013 

0.000000 

Any 



2008 

0.000314 

0.000606 

0.000317 

0.000218 


Appendix Table 1 

Regression Coefficients and Mean Values Used for Calculation of Real and Nominal Case-Mix Changes: 2000-2008 

 

 

Coefficients 

Means 

Real Case-Mix Change 
(2007) 

APR 
DRG 
Sev 

Level 

Variable 

IPS Period 

IPS 
Mean 

2007 
Mean 

(IPS Model) 

2007 
Mean 

(2008 model) 

2008 
Mean 

Based on 
IPS 
coefficients 

Based on 
2008 
coefficients 

Mod 

 

-0.19119 

0.06365 

0.000925 

0.001066 

0.001066 

0.001059 

-0.000027 

0.000000 

Major 

 

-0.1812 

0.01846 

0.000482 

0.000807 

0.000807 

0.000870 

-0.000059 

0.000001 

Any 

10 Electrolyte Disorders Except 
Hypovolemia Related 

0.05147 

0.05154 

0.005283 

0.006933 

0.006933 

0.007231 

0.000085 

0.000015 

Minor 

 

-0.04656 

-0.02548 

0.000597 

0.000737 

0.000737 

0.000752 

-0.000007 

0.000000 

Mod 

 

-0.01375 

0.01902 

0.003197 

0.003674 

0.003674 

0.003746 

-0.000007 

0.000001 

Major 

 

0.03698 

-0.02406 

0.001401 

0.002342 

0.002342 

0.002462 

0.000035 

-0.000003 

Any 

11 Kidney Transplant 

-0.09761 

-0.16484 

0.000335 

0.000418 

0.000418 

0.000418 

-0.000008 

0.000000 

Mod 

 

-0.07291 

-0.09485 

0.000156 

0.000155 

0.000155 

0.000134 

0.000000 

0.000002 

Major 

 

0.00476 

-0.01545 

0.000128 

0.000216 

0.000216 

0.000237 

0.000000 

0.000000 

 Any 

11 Major Bladder Procedures 

0.0038 

0.09451 

0.001133 

0.000915 

0.000915 

0.000856 

-0.000001 

-0.000006 

Mod 

 

-0.1502 

-0.19977 

0.000405 

0.000235 

0.000235 

0.000240 

0.000026 

-0.000001 

Major 

 

-0.16737 

-0.25614 

0.000654 

0.000566 

0.000566 

0.000493 

0.000015 

0.000019 

Any 

11 Kidney & Urinary Tract 
Procedures For Malignancy 

-0.05043 

-0.00274 

0.001110 

0.000957 

0.000957 

0.001051 

0.000008 

0.000000 

Minor 

 

-0.0373 

-0.08602 

0.000287 

0.000197 

0.000197 

0.000188 

0.000003 

0.000001 

Mod 

 

0.00701 

-0.05303 

0.000389 

0.000361 

0.000361 

0.000386 

0.000000 

-0.000001 

Major 

 

0.05191 

-0.11097 

0.000357 

0.000336 

0.000336 

0.000375 

-0.000001 

-0.000004 

Any 

11 Kidney & Urinary Tract 
Procedures For Nonmalignancy 

0.1281 

0.00651 

0.001311 

0.001070 

0.001070 

0.001016 

-0.000031 

0.000000 

Minor 

 

-0.19464 

-0.15489 

0.000255 

0.000141 

0.000141 

0.000139 

0.000022 

0.000000 

Mod 

 

-0.18175 

-0.1092 

0.000447 

0.000347 

0.000347 

0.000337 

0.000018 

0.000001 

Major 

 

-0.2516 

-0.12749 

0.000507 

0.000493 

0.000493 

0.000440 

0.000004 

0.000007 



2008 


Appendix Table 1 

Regression Coefficients and Mean Values Used for Calculation of Real and Nominal Case-Mix Changes: 2000-2008 

 

 

Coefficients 

Means 

Real Case-Mix Change 
(2007) 

APR 
DRG 
Sev 

Level 

Variable 

IPS Period 

IPS 
Mean 

2007 
Mean 

(IPS Model) 

2007 
Mean 

(2008 model) 

2008 
Mean 

Based on 
IPS 
coefficients 

Based on 
2008 
coefficients 

Any 

11 Renal Dialysis Access Device 
Procedure Only 

0.0038 

-0.06063 

0.001579 

0.001406 

0.001406 

0.001307 

-0.000001 

0.000006 

Minor 

 

0.04816 

-0.05907 

0.000191 

0.000064 

0.000064 

0.000019 

-0.000006 

0.000003 

Mod 

 

0.05035 

-0.03182 

0.000798 

0.000501 

0.000501 

0.000416 

-0.000015 

0.000003 

Major 

 

0.06738 

0.00336 

0.000546 

0.000733 

0.000733 

0.000759 

0.000013 

0.000000 

Any 

11 Other Bladder Procedures 

-0.5007 

0.20009 

0.000814 

0.000552 

0.000552 

0.000550 

0.000131 

0.000000 

Minor 

 

0.5474 

-0.25858 

0.000329 

0.000153 

0.000153 

0.000152 

-0.000096 

0.000000 

Mod 

 

0.55054 

-0.14359 

0.000281 

0.000234 

0.000234 

0.000214 

-0.000026 

0.000003 

Major 

 

0.65712 

-0.24066 

0.000198 

0.000148 

0.000148 

0.000159 

-0.000033 

-0.000003 

Any 

11 Urethral & Transurethral 
Procedures 

0.09169 

0.03043 

0.001487 

0.001403 

0.001403 

0.001412 

-0.000008 

0.000000 

Minor 

 

-0.08707 

-0.00229 

0.000309 

0.000257 

0.000257 

0.000201 

0.000005 

0.000000 

Mod 

 

-0.04472 

-0.01934 

0.000938 

0.000742 

0.000742 

0.000687 

0.000009 

0.000001 

Any 

11 Other Kidney, Urinary Tract & 
Related Procedures 

0.0845 

-0.07789 

0.001187 

0.001440 

0.001440 

0.001358 

0.000021 

0.000006 

Minor 

 

-0.05654 

-0.00388 

0.000160 

0.000155 

0.000155 

0.000124 

0.000000 

0.000000 

Mod 

 

-0.07899 

0.07946 

0.000549 

0.000454 

0.000454 

0.000439 

0.000007 

-0.000001 

Major 

 

-0.06204 

0.06858 

0.000386 

0.000679 

0.000679 

0.000654 

-0.000018 

-0.000002 

Any 

11 Renal Failure 

0.01888 

0.01095 

0.006706 

0.016224 

0.016224 

0.016784 

0.000180 

0.000006 

Minor 

 

0.03173 

-0.02947 

0.000121 

0.000041 

0.000041 

0.000017 

-0.000003 

0.000001 

Mod 

 

-0.02687 

0.0762 

0.001126 

0.000745 

0.000745 

0.000681 

0.000010 

-0.000005 

Major 

 

-0.01825 

0.04226 

0.005050 

0.014554 

0.014554 

0.014927 

-0.000173 

0.000016 

Any 

11 Kidney & Urinary Tract 
Malignancy 

-0.04585 

0.02235 

0.000233 

0.000229 

0.000229 

0.000204 

0.000000 

-0.000001 



2008 


Appendix Table 1 
-0.000027 

Regression Coefficients and Mean Values Used for Calculation of Real and Nominal Case-Mix Changes: 2000-2008 
0.000013 

Any 

12 Transurethral Prostatectomy 

0.02632 

-0.06743 

0.002989 

0.001949 

0.001949 

0.001752 

 

 

Coefficients 

Means 

Real Case-Mix Change 
(2007) 

APR 
DRG 
Sev 

Level 

Variable 

IPS Period 

IPS 
Mean 

2007 
Mean 

(IPS Model) 

2007 
Mean 

(2008 model) 

2008 
Mean 

Based on 
IPS 
coefficients 

Based on 
2008 
coefficients 

Major 

 

-0.11308 

-0.09757 

0.000128 

0.000114 

0.000114 

0.000113 

0.000002 

0.000000 

Any 

11 Nephritis & Nephrosis 

-0.06725 

0.01852 

0.000118 

0.000072 

0.000072 

0.000070 

0.000003 

0.000000 

Any 

11 Kidney & Urinary Tract Infections 

0.2772 

0.11469 

0.023267 

0.025415 

0.025415 

0.026272 

0.000595 

0.000098 

Minor 

 

-0.19348 

-0.03312 

0.001362 

0.001311 

0.001311 

0.001524 

0.000010 

-0.000007 

Mod 

 

-0.15011 

0.0101 

0.013042 

0.014011 

0.014011 

0.014196 

-0.000145 

0.000002 

Major 

 

-0.098 

0.00075016 

0.008435 

0.009395 

0.009395 

0.009803 

-0.000094 

0.000000 

Any 

11 Urinary Stones & Acquired Upper 
Urinary Tract Obstruction 

0.62128 

0.03121 

0.000756 

0.000885 

0.000885 

0.000870 

0.000080 

0.000000 

Minor 

 

-0.60379 

-0.13868 

0.000083 

0.000097 

0.000097 

0.000061 

-0.000009 

0.000005 

Mod 

 

-0.53576 

0.02836 

0.000482 

0.000507 

0.000507 

0.000516 

-0.000013 

0.000000 

Major 

 

-0.62226 

-0.03426 

0.000185 

0.000251 

0.000251 

0.000242 

-0.000041 

0.000000 

Any 

11 Malfunction, Reaction, Complic Of 
Genitourinary Device Or Proc 

-0.02099 

-0.12254 

0.003493 

0.004403 

0.004403 

0.004584 

-0.000019 

-0.000022 

Mod 

 

0.10188 

0.2257 

0.001257 

0.001006 

0.001006 

0.000905 

-0.000026 

-0.000023 

Major 

 

0.12537 

0.18356 

0.001930 

0.002326 

0.002326 

0.002448 

0.000050 

0.000022 

Extreme 

 

0.08014 

0.19758 

0.000274 

0.001038 

0.001038 

0.001214 

0.000061 

0.000035 

Any 

12 Major Male Pelvic Procedures 

-0.14206 

-0.00795 

0.000861 

0.000520 

0.000520 

0.000516 

0.000048 

0.000000 

Minor 

 

-0.02506 

-0.16614 

0.000498 

0.000288 

0.000288 

0.000259 

0.000005 

0.000005 

Mod 

 

0.05447 

-0.07531 

0.000306 

0.000173 

0.000173 

0.000205 

-0.000007 

-0.000002 

Any 

12 Penis Procedures 

0.29856 

-0.12099 

0.000246 

0.000185 

0.000185 

0.000186 

-0.000018 

0.000000 

Minor 

 

-0.29223 

-0.11959 

0.000115 

0.000050 

0.000050 

0.000046 

0.000019 

0.000001 

Mod 

 

-0.22426 

-0.05372 

0.000105 

0.000103 

0.000103 

0.000093 

0.000001 

0.000001 



2008 


Appendix Table 1 

Regression Coefficients and Mean Values Used for Calculation of Real and Nominal Case-Mix Changes: 2000-2008 

 
Minor 

 


Coefficients 
0.027 

Means 
-0.00309 

Real Case-Mix Change 
(2007) 
0.001085 

APR 
DRG 
Sev 
0.000733 

Level 
0.000711 

Variable 
-0.000009 

IPS Period 
0.000000 

0.000733 

IPS 
Mean 
Mod 

2007 
Mean 


(IPS Model) 
0.04861 

2007 
Mean 
0.04583 

(2008 model) 
0.001627 

2008 
Mean 
0.000992 

Based on 
IPS 
coefficients 
0.000992 

Based on 
2008 
coefficients 
0.000848 

-0.000031 

-0.000007 

Major 

 

-0.02344 

0.11796 

0.000233 

0.000206 

0.000206 

0.000163 

0.000001 

-0.000005 

Any 

12 Testes & Scrotal Procedures 

0.08948 

0.03914 

0.000160 

0.000093 

0.000093 

0.000085 

-0.000006 

0.000000 

Any 

12 Other Male Reproductive System 
& Related Procedures 

-0.12564 

-0.05069 

0.000278 

0.000188 

0.000188 

0.000177 

0.000011 

0.000001 

Mod 

 

0.02998 

-0.11186 

0.000099 

0.000072 

0.000072 

0.000068 

-0.000001 

0.000000 

Major 

 

0.04282 

-0.07098 

0.000108 

0.000075 

0.000075 

0.000057 

-0.000001 

0.000001 

Any 

12 Malignancy, Male Reproductive 
System 

-0.21935 

0.04294 

0.000367 

0.000135 

0.000135 

0.000170 

0.000051 

0.000001 

Mod 

 

0.23241 

-0.11424 

0.000195 

0.000056 

0.000056 

0.000094 

-0.000032 

-0.000004 

Major 

 

0.00982 

-0.12625 

0.000124 

0.000055 

0.000055 

0.000057 

-0.000001 

0.000000 

Any 

12 Male Reproductive System 
Diagnoses Except Malignancy 

0.13624 

0.16405 

0.000699 

0.000917 

0.000917 

0.000965 

0.000030 

0.000008 

Minor 

 

-0.26206 

-0.36992 

0.000080 

0.000075 

0.000075 

0.000115 

0.000001 

-0.000015 

Mod 

 

-0.11248 

-0.13748 

0.000412 

0.000497 

0.000497 

0.000505 

-0.000010 

-0.000001 

Major 

 

-0.14208 

-0.07393 

0.000191 

0.000316 

0.000316 

0.000312 

-0.000018 

0.000000 

Any 

13 Pelvic Evisceration, Radical 
Hysterectomy & Other Radical Gyn 
Procs 

-0.00647 

-0.00519 

0.000373 

0.000231 

0.000231 

0.000207 

0.000001 

0.000000 

Minor 

 

-0.13719 

-0.17455 

0.000131 

0.000052 

0.000052 

0.000038 

0.000011 

0.000003 

Mod 

 

-0.0066 

-0.22828 

0.000153 

0.000099 

0.000099 

0.000097 

0.000000 

0.000000 

Any 

13 Uterine & Adnexa Procedures For 
Ovarian & Adnexal Malignancy 

0.07812 

-0.0671 

0.000501 

0.000371 

0.000371 

0.000362 

-0.000010 

0.000001 



2008 


Appendix Table 1 

Regression Coefficients and Mean Values Used for Calculation of Real and Nominal Case-Mix Changes: 2000-2008 

 

 

Coefficients 

Means 

Real Case-Mix Change 
(2007) 

APR 
DRG 
Sev 

Level 

Variable 

IPS Period 

IPS 
Mean 

2007 
Mean 

(IPS Model) 

2007 
Mean 

(2008 model) 

2008 
Mean 

Based on 
IPS 
coefficients 

Based on 
2008 
coefficients 

Mod 

 

-0.22147 

-0.08648 

0.000278 

0.000134 

0.000134 

0.000158 

0.000032 

-0.000002 

Major 

 

-0.19183 

-0.115 

0.000172 

0.000170 

0.000170 

0.000136 

0.000000 

0.000004 

Any 

13 Uterine & Adnexa Procedures For 
Non-Ovarian & Non-Adnexal Malig 

-0.32511 

0.05466 

0.000858 

0.000833 

0.000833 

0.000792 

0.000008 

-0.000002 

Minor 

 

0.27117 

-0.13607 

0.000233 

0.000179 

0.000179 

0.000181 

-0.000014 

0.000000 

Mod 

 

0.30653 

-0.11876 

0.000495 

0.000459 

0.000459 

0.000411 

-0.000011 

0.000006 

Major 

 

0.36432 

-0.13724 

0.000124 

0.000163 

0.000163 

0.000171 

0.000014 

-0.000001 

Any 

13 Uterine & Adnexa Procedures For 
Non-Malignancy Except Leiomyoma 

-0.20766 

-0.05117 

0.001678 

0.001331 

0.001331 

0.001249 

0.000072 

0.000004 

Minor 

 

0.13418 

-0.0678 

0.000635 

0.000445 

0.000445 

0.000457 

-0.000025 

-0.000001 

Mod 

 

0.22395 

-0.00866 

0.000814 

0.000669 

0.000669 

0.000621 

-0.000032 

0.000000 

Major 

 

0.15676 

-0.08922 

0.000191 

0.000193 

0.000193 

0.000138 

0.000000 

0.000005 

Any 

13 Female Reproductive System 
Reconstructive Procedures 

0.07356 

-0.04061 

0.001366 

0.001024 

0.001024 

0.000910 

-0.000025 

0.000005 

Minor 

 

-0.13827 

-0.04066 

0.000785 

0.000473 

0.000473 

0.000419 

0.000043 

0.000002 

Mod 

 

-0.15367 

-0.04287 

0.000526 

0.000497 

0.000497 

0.000440 

0.000004 

0.000002 

Any 

13 Dilation & Curettage For Non-
Obstetric Diagnoses 

-0.0261 

-0.04823 

0.000144 

0.000121 

0.000121 

0.000121 

0.000001 

0.000000 

Any 

13 Other Female Reproductive 
System & Related Procedures 

-0.02677 

-0.11937 

0.000399 

0.000347 

0.000347 

0.000301 

0.000001 

0.000005 

Minor 

 

-0.03144 

0.15931 

0.000204 

0.000102 

0.000102 

0.000095 

0.000003 

-0.000001 

Mod 

 

-0.13708 

0.04522 

0.000147 

0.000158 

0.000158 

0.000121 

-0.000002 

-0.000002 

Any 

13 Uterine & Adnexa Procedures For 
Leiomyoma 

0.36233 

-0.03616 

0.000223 

0.000232 

0.000232 

0.000273 

0.000003 

-0.000001 



2008 


Appendix Table 1 

Regression Coefficients and Mean Values Used for Calculation of Real and Nominal Case-Mix Changes: 2000-2008 

 

 

Coefficients 

Means 

Real Case-Mix Change 
(2007) 

APR 
DRG 
Sev 

Level 

Variable 

IPS Period 

IPS 
Mean 

2007 
Mean 

(IPS Model) 

2007 
Mean 

(2008 model) 

2008 
Mean 

Based on 
IPS 
coefficients 

Based on 
2008 
coefficients 

Minor 

 

-0.38328 

-0.14503 

0.000089 

0.000101 

0.000101 

0.000141 

-0.000004 

-0.000006 

Mod 

 

-0.42493 

0.00883 

0.000124 

0.000099 

0.000099 

0.000104 

0.000011 

0.000000 

Any 

13 Female Reproductive System 
Malignancy 

-0.17391 

-0.05707 

0.000309 

0.000202 

0.000202 

0.000194 

0.000019 

0.000000 

Mod 

 

0.05397 

0.01596 

0.000156 

0.000074 

0.000074 

0.000076 

-0.000004 

0.000000 

Major 

 

0.06987 

-0.03601 

0.000137 

0.000086 

0.000086 

0.000089 

-0.000004 

0.000000 

Any 

13 Female Reproductive System 
Infections 

0.05841 

0.07032 

0.000322 

0.000389 

0.000389 

0.000369 

0.000004 

-0.000001 

Mod 

 

0.22322 

-0.05266 

0.000175 

0.000149 

0.000149 

0.000164 

-0.000006 

-0.000001 

Major 

 

-0.00222 

-0.03141 

0.000108 

0.000209 

0.000209 

0.000164 

0.000000 

0.000001 

Any 

13 Menstrual & Other Female 
Reproductive System Disorders 

-0.00542 

-0.0671 

0.000204 

0.000250 

0.000250 

0.000258 

0.000000 

-0.000001 

Mod 

 

-0.00877 

0.14485 

0.000131 

0.000148 

0.000148 

0.000148 

0.000000 

0.000000 

Any 

16 Splenectomy 

-0.05058 

-0.1015 

0.000169 

0.000130 

0.000130 

0.000101 

0.000002 

0.000003 

Any 

16 Other Procedures Of Blood & 
Blood-Forming Organs 

-0.12197 

-0.20034 

0.000080 

0.000095 

0.000095 

0.000102 

-0.000002 

-0.000001 

Any 

16 Major Hematologic/Immunologic 
Diag Exc Sickle Cell Crisis & Coagul 

-0.04088 

0.12146 

0.001567 

0.001122 

0.001122 

0.001097 

0.000018 

-0.000003 

Minor 

 

-0.12216 

-0.07229 

0.000131 

0.000049 

0.000049 

0.000041 

0.000010 

0.000001 

Mod 

 

-0.06552 

-0.07417 

0.000798 

0.000508 

0.000508 

0.000445 

0.000019 

0.000005 

Major 

 

0.0233 

-0.12 

0.000606 

0.000494 

0.000494 

0.000515 

-0.000003 

-0.000002 

Any 

16 Coagulation & Platelet Disorders 

0.06996 

-0.0075 

0.001270 

0.000878 

0.000878 

0.000778 

-0.000027 

0.000001 

Minor 

 

-0.07955 

0.10721 

0.000571 

0.000319 

0.000319 

0.000272 

0.000020 

-0.000005 

Mod 

 

-0.03068 

-0.01119 

0.000501 

0.000339 

0.000339 

0.000288 

0.000005 

0.000001 



2008 


Appendix Table 1 

Regression Coefficients and Mean Values Used for Calculation of Real and Nominal Case-Mix Changes: 2000-2008 

 

 

Coefficients 

Means 

Real Case-Mix Change 
(2007) 

APR 
DRG 
Sev 

Level 

Variable 

IPS Period 

IPS 
Mean 

2007 
Mean 

(IPS Model) 

2007 
Mean 

(2008 model) 

2008 
Mean 

Based on 
IPS 
coefficients 

Based on 
2008 
coefficients 

Major 

 

-0.03252 

0.02584 

0.000153 

0.000163 

0.000163 

0.000181 

0.000000 

0.000000 

Any 

16 Other Anemia & Disorders Of 
Blood & Blood-Forming Organs 

-0.1025 

0.11692 

0.004629 

0.006980 

0.006980 

0.007055 

-0.000241 

0.000009 

Minor 

 

0.08175 

-0.05931 

0.001870 

0.002058 

0.002058 

0.002057 

0.000015 

0.000000 

Mod 

 

0.09292 

-0.0635 

0.001870 

0.003061 

0.003061 

0.003009 

0.000111 

0.000003 

Major 

 

0.07444 

-0.08766 

0.000829 

0.001649 

0.001649 

0.001749 

0.000061 

-0.000009 

Any 

17 Major O.R. Procedures For 
Lymphatic/Hematopoietic/Other 
Neoplasms 

0.06619 

-0.09875 

0.000453 

0.000434 

0.000434 

0.000338 

-0.000001 

0.000009 

Mod 

 

-0.13016 

0.03597 

0.000195 

0.000186 

0.000186 

0.000119 

0.000001 

-0.000002 

Major 

 

-0.15658 

0.02481 

0.000147 

0.000139 

0.000139 

0.000130 

0.000001 

0.000000 

Any 

17 Other O.R. Procedures For 
Lymphatic/Hematopoietic/Other 
Neoplasms 

0.19687 

-0.18759 

0.000689 

0.000533 

0.000533 

0.000512 

-0.000031 

0.000004 

Minor 

 

-0.29409 

0.07631 

0.000169 

0.000098 

0.000098 

0.000092 

0.000021 

-0.000001 

Mod 

 

-0.25614 

0.03692 

0.000348 

0.000247 

0.000247 

0.000213 

0.000026 

-0.000001 

Major 

 

-0.20635 

0.13479 

0.000147 

0.000154 

0.000154 

0.000171 

-0.000001 

0.000002 

Any 

17 Acute Leukemia 

-0.2478 

-0.03481 

0.000294 

0.000182 

0.000182 

0.000143 

0.000028 

0.000001 

Mod 

 

0.09013 

-0.19884 

0.000080 

0.000056 

0.000056 

0.000038 

-0.000002 

0.000004 

Major 

 

0.17244 

-0.06946 

0.000128 

0.000076 

0.000076 

0.000071 

-0.000009 

0.000000 

Any 

17 Lymphoma, Myeloma & Non-
Acute Leukemia 

0.15584 

0.02903 

0.001570 

0.000967 

0.000967 

0.000887 

-0.000094 

-0.000002 

Minor 

 

-0.29222 

-0.06568 

0.000089 

0.000073 

0.000073 

0.000033 

0.000005 

0.000003 

Mod 

 

-0.18952 

-0.00669 

0.000718 

0.000350 

0.000350 

0.000316 

0.000070 

0.000000 



2008 


Appendix Table 1 

Regression Coefficients and Mean Values Used for Calculation of Real and Nominal Case-Mix Changes: 2000-2008 

 

 

Coefficients 

Means 

Real Case-Mix Change 
(2007) 

APR 
DRG 
Sev 

Level 

Variable 

IPS Period 

IPS 
Mean 

2007 
Mean 

(IPS Model) 

2007 
Mean 

(2008 model) 

2008 
Mean 

Based on 
IPS 
coefficients 

Based on 
2008 
coefficients 

Major 

 

-0.26594 

0.01338 

0.000644 

0.000442 

0.000442 

0.000450 

0.000054 

0.000000 

Any 

17 Radiotherapy 

-0.10251 

0.02933 

0.000160 

0.000103 

0.000103 

0.000081 

0.000006 

-0.000001 

Mod 

 

0.30459 

0.30418 

0.000121 

0.000072 

0.000072 

0.000054 

-0.000015 

-0.000005 

Any 

17 Chemotherapy 

-0.1196 

-0.1281 

0.001496 

0.000701 

0.000701 

0.000641 

0.000095 

0.000008 

Minor 

 

0.00365 

0.00278 

0.000657 

0.000266 

0.000266 

0.000207 

-0.000001 

0.000000 

Mod 

 

0.07576 

0.1272 

0.000619 

0.000270 

0.000270 

0.000282 

-0.000026 

0.000002 

Major 

 

-0.02195 

0.07626 

0.000134 

0.000124 

0.000124 

0.000125 

0.000000 

0.000000 

Any 

17 Lymphatic & Other Malignancies & 
Neoplasms Of Uncertain Behavior 

-0.05927 

-0.09021 

0.000948 

0.000626 

0.000626 

0.000628 

0.000019 

0.000000 

Minor 

 

-0.0541 

0.3777 

0.000080 

0.000040 

0.000040 

0.000034 

0.000002 

-0.000002 

Mod 

 

0.0428 

0.02647 

0.000402 

0.000231 

0.000231 

0.000289 

-0.000007 

0.000002 

Major 

 

0.05568 

0.10386 

0.000424 

0.000309 

0.000309 

0.000264 

-0.000006 

-0.000005 

 Any 

18 Infectious & Parasitic Diseases 
Including Hiv W O.R. Procedure 

-0.13565 

0.01564 

0.001643 

0.002609 

0.002609 

0.002792 

-0.000131 

0.000003 

Mod 

 

0.24315 

-0.0589 

0.000434 

0.000282 

0.000282 

0.000252 

-0.000037 

0.000002 

Major 

 

0.26109 

-0.00443 

0.000852 

0.001105 

0.001105 

0.001077 

0.000066 

0.000000 

Extreme 

 

0.18815 

-0.00118 

0.000335 

0.001204 

0.001204 

0.001444 

0.000164 

0.000000 

Any 

18 Post-Op, Post-Trauma, Other 
Device Infections W O.R. Procedure 

-0.03992 

-0.03237 

0.002131 

0.002048 

0.002048 

0.002048 

0.000003 

0.000000 

Minor 

 

-0.0008765 

-0.14594 

0.000278 

0.000284 

0.000284 

0.000257 

0.000000 

0.000004 

Mod 

 

0.01401 

-0.06066 

0.000932 

0.000870 

0.000870 

0.000842 

-0.000001 

0.000002 

Major 

 

0.09548 

-0.00314 

0.000724 

0.000678 

0.000678 

0.000682 

-0.000004 

0.000000 

Any 

18 Septicemia & Disseminated 
Infections 

0.05778 

0.07565 

0.014494 

0.018500 

0.018500 

0.020449 

0.000231 

0.000147 



2008 


Appendix Table 1 

Regression Coefficients and Mean Values Used for Calculation of Real and Nominal Case-Mix Changes: 2000-2008 

 

 

Coefficients 

Means 

Real Case-Mix Change 
(2007) 

APR 
DRG 
Sev 

Level 

Variable 

IPS Period 

IPS 
Mean 

2007 
Mean 

(IPS Model) 

2007 
Mean 

(2008 model) 

2008 
Mean 

Based on 
IPS 
coefficients 

Based on 
2008 
coefficients 

Minor 

 

-0.0685 

0.05206 

0.000204 

0.000238 

0.000238 

0.000227 

-0.000002 

-0.000001 

Mod 

 

0.03276 

0.0208 

0.006192 

0.005021 

0.005021 

0.005070 

-0.000038 

0.000001 

Major 

 

0.03394 

0.01379 

0.006741 

0.008452 

0.008452 

0.009013 

0.000058 

0.000008 

Any 

18 Post-Operative, Post-Traumatic, 
Other Device Infections 

-0.16361 

0.02269 

0.004297 

0.004172 

0.004172 

0.003933 

0.000020 

-0.000005 

Minor 

 

0.05096 

-0.06653 

0.000960 

0.000711 

0.000711 

0.000618 

-0.000013 

0.000006 

Mod 

 

0.12858 

-0.05908 

0.002221 

0.002061 

0.002061 

0.001844 

-0.000021 

0.000013 

Major 

 

0.11966 

-0.02911 

0.000983 

0.001159 

0.001159 

0.001189 

0.000021 

-0.000001 

Any 

18 Fever 

-0.10893 

0.0792 

0.001046 

0.001048 

0.001048 

0.001049 

0.000000 

0.000000 

Minor 

 

0.1742 

-0.03905 

0.000108 

0.000073 

0.000073 

0.000109 

-0.000006 

-0.000001 

Mod 

 

0.14572 

0.03743 

0.000619 

0.000577 

0.000577 

0.000578 

-0.000006 

0.000000 

Major 

 

0.26241 

-0.04474 

0.000313 

0.000365 

0.000365 

0.000325 

0.000014 

0.000002 

Any 

18 Viral Illness 

0.30241 

-0.01047 

0.000762 

0.000656 

0.000656 

0.000803 

-0.000032 

-0.000002 

Minor 

 

-0.28522 

0.17872 

0.000093 

0.000033 

0.000033 

0.000030 

0.000017 

-0.000001 

Mod 

 

-0.24571 

0.03903 

0.000453 

0.000386 

0.000386 

0.000370 

0.000017 

-0.000001 

Major 

 

-0.3473 

0.05034 

0.000201 

0.000218 

0.000218 

0.000370 

-0.000006 

0.000008 

Any 

18 Other Infectious & Parasitic 
Diseases 

0.27446 

-0.00185 

0.001085 

0.001367 

0.001367 

0.001286 

0.000078 

0.000000 

Minor 

 

-0.21646 

-0.01645 

0.000236 

0.000316 

0.000316 

0.000285 

-0.000017 

0.000001 

Mod 

 

-0.26738 

0.05325 

0.000475 

0.000638 

0.000638 

0.000586 

-0.000043 

-0.000003 

Major 

 

-0.31766 

-0.04695 

0.000303 

0.000249 

0.000249 

0.000251 

0.000017 

0.000000 

Any 

19 Mental Illness Diagnosis W O.R. 
Procedure 

0.23463 

-0.22069 

0.000083 

0.000045 

0.000045 

0.000060 

-0.000009 

-0.000003 



2008 


Appendix Table 1 

Regression Coefficients and Mean Values Used for Calculation of Real and Nominal Case-Mix Changes: 2000-2008 

 

 

Coefficients 

Means 

Real Case-Mix Change 
(2007) 

APR 
DRG 
Sev 

Level 

Variable 

IPS Period 

IPS 
Mean 

2007 
Mean 

(IPS Model) 

2007 
Mean 

(2008 model) 

2008 
Mean 

Based on 
IPS 
coefficients 

Based on 
2008 
coefficients 

Any 

19 Schizophrenia 

-0.52967 

0.1308 

0.002578 

0.003585 

0.003585 

0.003828 

-0.000533 

0.000032 

Minor 

 

0.16307 

-0.31749 

0.000756 

0.000869 

0.000869 

0.000902 

0.000018 

-0.000011 

Mod 

 

0.26682 

-0.2575 

0.001681 

0.002389 

0.002389 

0.002586 

0.000189 

-0.000051 

Major 

 

0.37919 

-0.2269 

0.000124 

0.000303 

0.000303 

0.000307 

0.000068 

-0.000001 

Any 

19 Major Depressive Disorders & 
Other/Unspecified Psychoses 

-0.1418 

0.0767 

0.007067 

0.005563 

0.005563 

0.005658 

0.000213 

0.000007 

Minor 

 

0.02758 

-0.12548 

0.000223 

0.000237 

0.000237 

0.000203 

0.000000 

0.000004 

Mod 

 

0.11288 

-0.00763 

0.005510 

0.004238 

0.004238 

0.004268 

-0.000144 

0.000000 

Major 

 

0.1287 

-0.03072 

0.001046 

0.000861 

0.000861 

0.000948 

-0.000024 

-0.000003 

Any 

19 Bipolar Disorders 

-0.14582 

0.11424 

0.001713 

0.002210 

0.002210 

0.002394 

-0.000072 

0.000021 

Minor 

 

-0.15147 

-0.16354 

0.000265 

0.000367 

0.000367 

0.000364 

-0.000016 

0.000000 

Mod 

 

0.03475 

-0.13242 

0.001295 

0.001520 

0.001520 

0.001717 

0.000008 

-0.000026 

Major 

 

0.06594 

-0.20106 

0.000131 

0.000250 

0.000250 

0.000241 

0.000008 

0.000002 

Any 

19 Depression Except Major 
Depressive Disorder 

0.1936 

0.04067 

0.000884 

0.000648 

0.000648 

0.000594 

-0.000046 

-0.000002 

Minor 

 

-0.42514 

0.06274 

0.000096 

0.000106 

0.000106 

0.000105 

-0.000004 

0.000000 

Mod 

 

-0.21887 

-0.01374 

0.000718 

0.000454 

0.000454 

0.000392 

0.000058 

0.000001 

Any 

19 Adjustment Disorders & Neuroses 
Except Depressive Diagnoses 

-0.19965 

-0.14443 

0.000185 

0.000134 

0.000134 

0.000150 

0.000010 

-0.000002 

Minor 

 

0.1135 

0.25941 

0.000089 

0.000062 

0.000062 

0.000069 

-0.000003 

0.000002 

Mod 

 

0.18339 

0.20293 

0.000080 

0.000065 

0.000065 

0.000071 

-0.000003 

0.000001 

Any 

19 Acute Anxiety & Delirium States 

-0.13778 

-0.26093 

0.001678 

0.000887 

0.000887 

0.000721 

0.000109 

0.000043 

Minor 

 

0.0603 

0.26552 

0.000526 

0.000334 

0.000334 

0.000283 

-0.000012 

-0.000014 



2008 


Appendix Table 1 

Regression Coefficients and Mean Values Used for Calculation of Real and Nominal Case-Mix Changes: 2000-2008 

 

 

Coefficients 

Means 

Real Case-Mix Change 
(2007) 

APR 
DRG 
Sev 

Level 

Variable 

IPS Period 

IPS 
Mean 

2007 
Mean 

(IPS Model) 

2007 
Mean 

(2008 model) 

2008 
Mean 

Based on 
IPS 
coefficients 

Based on 
2008 
coefficients 

0.01337 

0.000967 

0.000861 

0.000861 

0.000857 

0.000009 

0.000000 

Any 

20 Other Drug Abuse & Dependence 

-0.0893 

Minor 

 

0.03165 

0.000102 

0.000063 

0.000063 

0.000065 

-0.000009 

0.000000 

0.22062 

Mod 

 

0.08183 

0.000597 

0.000483 

0.000483 

0.000496 

-0.000021 

0.000001 

0.18428 

Major 

 

0.15537 

0.000255 

0.000289 

0.000289 

0.000265 

0.000009 

-0.000004 

0.27851 

Any 

21 O.R. Procedure For Other 
Complications Of Treatment 

-0.18301 

-0.03645 

0.001866 

0.001725 

0.001725 

0.001742 

0.000005 

-0.000003 

Mod 

 

0.25635 

0.34546 

0.000788 

0.000393 

0.000393 

0.000313 

-0.000101 

-0.000028 

Major 

 

0.24339 

0.44766 

0.000338 

0.000152 

0.000152 

0.000112 

-0.000045 

-0.000018 

Any 

19 Organic Mental Health 
Disturbances 

0.21646 

0.17446 

0.005216 

0.003083 

0.003083 

0.003117 

-0.000462 

0.000006 

Minor 

 

-0.17276 

-0.07119 

0.001761 

0.000645 

0.000645 

0.000602 

0.000193 

0.000003 

Mod 

 

-0.15738 

-0.08015 

0.002674 

0.001781 

0.001781 

0.001899 

0.000141 

-0.000009 

Major 

 

-0.102 

-0.10737 

0.000759 

0.000620 

0.000620 

0.000581 

0.000014 

0.000004 

Any 

19 Other Mental Health Disorders 

-0.02406 

-0.15408 

0.000354 

0.000271 

0.000271 

0.000327 

0.000002 

-0.000009 

Minor 

 

0.09665 

0.23757 

0.000083 

0.000025 

0.000025 

0.000039 

-0.000006 

0.000003 

Mod 

 

0.11724 

0.14118 

0.000207 

0.000193 

0.000193 

0.000227 

-0.000002 

0.000005 

Any 

20 Alcohol & Drug Dependence W 
Rehab Or Rehab/Detox Therapy 

-0.14321 

0.0334 

0.000083 

0.000103 

0.000103 

0.000123 

-0.000003 

0.000001 

Any 

20 Alcohol Abuse & Dependence 

-0.00301 

-0.04153 

0.000530 

0.000599 

0.000599 

0.000621 

0.000000 

-0.000001 

Mod 

 

0.00098008 

0.06378 

0.000341 

0.000330 

0.000330 

0.000353 

0.000000 

0.000001 

Major 

 

-0.16142 

0.00539 

0.000102 

0.000164 

0.000164 

0.000165 

-0.000010 

0.000000 

Minor 

 

-0.00593 

0.15685 

0.000367 

0.000236 

0.000236 

0.000206 

0.000001 

-0.000005 

Mod 

 

0.01173 

0.1861 

0.000909 

0.000788 

0.000788 

0.000831 

-0.000001 

0.000008 



2008 


Appendix Table 1 

Regression Coefficients and Mean Values Used for Calculation of Real and Nominal Case-Mix Changes: 2000-2008 

 

 

Coefficients 

Means 

Real Case-Mix Change 
(2007) 

APR 
DRG 
Sev 

Level 

Variable 

IPS Period 

IPS 
Mean 

2007 
Mean 

(IPS Model) 

2007 
Mean 

(2008 model) 

2008 
Mean 

Based on 
IPS 
coefficients 

Based on 
2008 
coefficients 

Major 

 

0.09849 

0.16565 

0.000475 

0.000516 

0.000516 

0.000539 

0.000004 

0.000004 

Any 

21 Allergic Reactions 

0.134 

0.0309 

0.000182 

0.000338 

0.000338 

0.000372 

0.000021 

0.000001 

Mod 

 

-0.10884 

-0.00719 

0.000093 

0.000162 

0.000162 

0.000173 

-0.000008 

0.000000 

Any 

21 Poisoning Of Medicinal Agents 

0.06752 

0.05751 

0.001761 

0.002114 

0.002114 

0.002308 

0.000024 

0.000011 

Minor 

 

-0.13046 

-0.0353 

0.000128 

0.000112 

0.000112 

0.000146 

0.000002 

-0.000001 

Mod 

 

-0.07502 

-0.04148 

0.000992 

0.001001 

0.001001 

0.001137 

-0.000001 

-0.000006 

Major 

 

-0.0667 

-0.03199 

0.000581 

0.000801 

0.000801 

0.000800 

-0.000015 

0.000000 

Any 

21 Other Complications Of Treatment 

0.41196 

0.05477 

0.001930 

0.002086 

0.002086 

0.002017 

0.000064 

-0.000004 

Minor 

 

-0.41494 

-0.07571 

0.000428 

0.000310 

0.000310 

0.000300 

0.000049 

0.000001 

Mod 

 

-0.41327 

-0.04761 

0.000973 

0.000959 

0.000959 

0.000901 

0.000006 

0.000003 

Major 

 

-0.35757 

-0.03644 

0.000485 

0.000700 

0.000700 

0.000705 

-0.000077 

0.000000 

Any 

21 Other Injury, Poisoning & Toxic 
Effect Diagnoses 

0.39773 

0.17752 

0.000475 

0.000407 

0.000407 

0.000392 

-0.000027 

-0.000003 

Minor 

 

-0.27559 

-0.16832 

0.000118 

0.000088 

0.000088 

0.000086 

0.000008 

0.000000 

Mod 

 

-0.2959 

-0.10899 

0.000201 

0.000192 

0.000192 

0.000182 

0.000003 

0.000001 

Major 

 

-0.37748 

-0.28308 

0.000124 

0.000114 

0.000114 

0.000097 

0.000004 

0.000005 

Any 

21 Toxic Effects Of Non-Medicinal 
Substances 

-0.08727 

0.00685 

0.000182 

0.000329 

0.000329 

0.000324 

-0.000013 

0.000000 

Mod 

 

0.17377 

0.09349 

0.000086 

0.000131 

0.000131 

0.000136 

0.000008 

0.000000 

Any 

22 Full Thickness Burns W Skin Graft 

0.43158 

0.18024 

0.000252 

0.000134 

0.000134 

0.000117 

-0.000051 

-0.000003 

Mod 

 

-0.48957 

-0.10757 

0.000121 

0.000057 

0.000057 

0.000036 

0.000031 

0.000002 

Major 

 

-0.08129 

-0.04619 

0.000093 

0.000049 

0.000049 

0.000049 

0.000004 

0.000000 



2008 


Appendix Table 1 

Regression Coefficients and Mean Values Used for Calculation of Real and Nominal Case-Mix Changes: 2000-2008 

 

 

Coefficients 

Means 

Real Case-Mix Change 
(2007) 

APR 
DRG 
Sev 

Level 

Variable 

IPS Period 

IPS 
Mean 

2007 
Mean 

(IPS Model) 

2007 
Mean 

(2008 model) 

2008 
Mean 

Based on 
IPS 
coefficients 

Based on 
2008 
coefficients 

Any 

22 Extensive 3Rd Degree Or Full 
Thickness Burns W/O Skin Graft 

-0.0229 

0.11331 

0.000175 

0.000096 

0.000096 

0.000092 

0.000002 

-0.000001 

Mod 

 

-0.05638 

-0.10247 

0.000093 

0.000054 

0.000054 

0.000041 

0.000002 

0.000001 

Any 

22 Partial Thickness Burns W Or 
W/O Skin Graft 

0.00031758 

-0.11712 

0.000281 

0.000217 

0.000217 

0.000225 

0.000000 

-0.000001 

Mod 

 

0.04066 

0.1484 

0.000182 

0.000090 

0.000090 

0.000088 

-0.000004 

0.000000 

Any 

23 Procedure W Diag Of Rehab, 
Aftercare Or Oth Contact W Health 
Service 

0.2198 

0.06829 

0.000227 

0.000286 

0.000286 

0.000256 

0.000013 

-0.000002 

Minor 

 

-0.21107 

-0.13899 

0.000150 

0.000102 

0.000102 

0.000115 

0.000010 

-0.000002 

Any 

23 Rehabilitation 

0.66989 

0.20215 

0.002099 

0.001290 

0.001290 

0.001341 

-0.000542 

0.000010 

Minor 

 

-0.43636 

0.0154 

0.000341 

0.000238 

0.000238 

0.000252 

0.000045 

0.000000 

Mod 

 

-0.43173 

0.0219 

0.000992 

0.000650 

0.000650 

0.000617 

0.000148 

-0.000001 

Major 

 

-0.23122 

0.07951 

0.000673 

0.000348 

0.000348 

0.000414 

0.000075 

0.000005 

Any 

23 Signs, Symptoms & Other Factors 
Influencing Health Status 

-0.25563 

0.23715 

0.002686 

0.004897 

0.004897 

0.005743 

-0.000565 

0.000201 

Minor 

 

0.36536 

-0.1171 

0.000475 

0.000645 

0.000645 

0.000730 

0.000062 

-0.000010 

Mod 

 

0.35875 

-0.10347 

0.001895 

0.003170 

0.003170 

0.003609 

0.000457 

-0.000045 

Major 

 

0.32604 

-0.11668 

0.000313 

0.001030 

0.001030 

0.001293 

0.000234 

-0.000031 

Any 

23 Other Aftercare & Convalescence 

-0.02102 

0.07914 

0.000112 

0.000173 

0.000173 

0.000180 

-0.000001 

0.000001 

Any 

24 Hiv W Multiple Major Hiv Related 
Conditions 

-0.18478 

-0.10905 

0.000128 

0.000158 

0.000158 

0.000138 

-0.000006 

0.000002 

Any 

24 Hiv W Major Hiv Related 
Condition 

-0.13662 

0.01987 

0.000274 

0.000233 

0.000233 

0.000212 

0.000006 

0.000000 

Major 

 

-0.00541 

-0.07165 

0.000160 

0.000148 

0.000148 

0.000134 

0.000000 

0.000001 



2008 


Appendix Table 1 

Regression Coefficients and Mean Values Used for Calculation of Real and Nominal Case-Mix Changes: 2000-2008 

 

 

Coefficients 

Means 

Real Case-Mix Change 
(2007) 

APR 
DRG 
Sev 

Level 

Variable 

IPS Period 

IPS 
Mean 

2007 
Mean 

(IPS Model) 

2007 
Mean 

(2008 model) 

2008 
Mean 

Based on 
IPS 
coefficients 

Based on 
2008 
coefficients 

Any 

24 Hiv W One Signif Hiv Cond Or 
W/O Signif Related Cond 

-0.09393 

0.0425 

0.000220 

0.000181 

0.000181 

0.000213 

0.000004 

0.000001 

Mod 

 

-0.0264 

-0.15764 

0.000115 

0.000102 

0.000102 

0.000124 

0.000000 

-0.000004 

Any 

25 Musculoskeletal & Other 
Procedures For Multiple Significant 
Trauma 

0.24488 

0.12109 

0.000542 

0.000652 

0.000652 

0.000723 

0.000027 

0.000009 

Mod 

 

0.06123 

0.08782 

0.000242 

0.000218 

0.000218 

0.000237 

-0.000001 

0.000002 

Major 

 

0.1112 

-0.04704 

0.000214 

0.000314 

0.000314 

0.000358 

0.000011 

-0.000002 

Any 

25 Multiple Significant Trauma W/O 
O.R. Procedure 

0.20028 

0.03445 

0.000290 

0.000494 

0.000494 

0.000432 

0.000041 

-0.000002 

Mod 

 

0.04338 

0.15146 

0.000156 

0.000204 

0.000204 

0.000195 

0.000002 

-0.000001 

Major 

 

-0.12974 

0.00982 

0.000108 

0.000231 

0.000231 

0.000194 

-0.000016 

0.000000 

Any 

Extensive Procedure Unrelated To 
Principal Diagnosis 

0.09132 

0.09184 

0.002249 

0.002004 

0.002004 

0.001945 

-0.000022 

-0.000005 

Minor 

 

0.00727 

-0.13812 

0.000156 

0.000072 

0.000072 

0.000063 

-0.000001 

0.000001 

Mod 

 

-0.02153 

0.02897 

0.000648 

0.000444 

0.000444 

0.000424 

0.000004 

-0.000001 

Major 

 

0.08518 

-0.00902 

0.001050 

0.001006 

0.001006 

0.000909 

-0.000004 

0.000001 

Any 

Moderately Extensive Procedure 
Unrelated To Principal Diagnosis 

0.08974 

-0.00944 

0.002737 

0.002916 

0.002916 

0.003297 

0.000016 

-0.000004 

Minor 

 

-0.01413 

0.08104 

0.000124 

0.000110 

0.000110 

0.000100 

0.000000 

-0.000001 

Mod 

 

-0.02473 

0.07131 

0.000871 

0.000805 

0.000805 

0.000827 

0.000002 

0.000002 

Major 

 

0.00949 

0.05386 

0.001404 

0.001400 

0.001400 

0.001650 

0.000000 

0.000013 

Any 

Nonextensive Procedure Unrelated 
To Principal Diagnosis 

0.18751 

-0.00191 

0.003267 

0.002325 

0.002325 

0.002071 

-0.000177 

0.000000 

Minor 

 

-0.1752 

-0.13871 

0.000284 

0.000155 

0.000155 

0.000133 

0.000023 

0.000003 



2008 


Appendix Table 1 

Regression Coefficients and Mean Values Used for Calculation of Real and Nominal Case-Mix Changes: 2000-2008 

 

 

Coefficients 

Means 

Real Case-Mix Change 
(2007) 

APR 
DRG 
Sev 

Level 

Variable 

IPS Period 

IPS 
Mean 

2007 
Mean 

(IPS Model) 

2007 
Mean 

(2008 model) 

2008 
Mean 

Based on 
IPS 
coefficients 

Based on 
2008 
coefficients 

Mod 

 

-0.152 

-0.02114 

0.001391 

0.000815 

0.000815 

0.000688 

0.000087 

0.000003 

Major 

 

-0.0973 

-0.00939 

0.001369 

0.001066 

0.001066 

0.000956 

0.000029 

0.000001 

 

Free-Standing Vol/NP 

-0.14221 

-0.00202 

0.158493 

0.115547 

0.115547 

0.107286 

0.006107 

0.000017 

 

Free-Standing Proprietary 

-0.08207 

0.1026 

0.040565 

0.072878 

0.072878 

0.077890 

-0.002652 

0.000514 

 

Free-Standing Government 

-0.13322 

-0.00299 

0.038689 

0.018570 

0.018570 

0.016254 

0.002680 

0.000007 

 

Facility-Based Vol/NP 

-0.14481 

-0.02465 

0.299250 

0.136032 

0.136032 

0.117245 

0.023636 

0.000463 

 

Facility-Based Proprietary 

-0.11309 

0.04423 

0.036217 

0.012954 

0.012954 

0.013092 

0.002631 

0.000006 

 

Facility-Based Government 

-0.153 

-0.02804 

0.041200 

0.020685 

0.020685 

0.019381 

0.003139 

0.000037 

 

Other Vol/NP 

-0.11094 

0.03959 

0.088324 

0.078100 

0.078100 

0.072086 

0.001134 

-0.000238 

 

Other Proprietary 

-0.09851 

0.12947 

0.292672 

0.539954 

0.539954 

0.572082 

-0.024360 

0.004160 

 

Other Government 

-0.11499 

0.05356 

0.004406 

0.004689 

0.004689 

0.004672 

-0.000033 

-0.000001 

 

Acute Care Hospital Payments in 120 
Days Preceding Home Health 
Episode 

-2.06E-06 

-1.94E-06 

$7,569.96 

$6,159.58 

$7,979.46 

$7,753.60 

0.002905 

0.000438 

 

Long Term Care Hospital Payments 
in 120 Days Preceding Home Health 
Episode 

-2.399E-07 

7.0454E-07 

$214.01 

$316.43 

$381.19 

$367.96 

-0.000025 

-0.000009 

 

Rehabilitation Facility Payments in 
120 Days Preceding Home Health 
Episode 

0.00000199 

0.00000329 

$799.97 

$725.61 

$923.77 

$863.94 

-0.000148 

-0.000197 

 

Medicare SNF Payments in 120 Days 
Preceding Home Health Episode 

0.00000915 

0.00000131 

$1,164.79 

$1,620.68 

$2,151.44 

$2,253.75 

0.004171 

0.000134 

Notes: 

1. Two regression models were estimatedone using data from the IPS period that was used to predict case-mix change for the period that the 80 HHRG model 
was used and a second using data from 2008 that was used to predict 2007-2008 case-mix levels under the 153 HHRG model. 

2. 2007 mean values for the Medicare payment variables differ for the IPS-2007 and the 2007-2008 analyses because of the use of different deflation factors for 



2008 


Appendix Table 1 

Regression Coefficients and Mean Values Used for Calculation of Real and Nominal Case-Mix Changes: 2000-2008 

 

 

Coefficients 

Means 

Real Case-Mix Change 
(2007) 

APR 
DRG 
Sev 

Level 

Variable 

IPS Period 

IPS 
Mean 

2007 
Mean 

(IPS Model) 

2007 
Mean 

(2008 model) 

2008 
Mean 

Based on 
IPS 
coefficients 

Based on 
2008 
coefficients 

Medicare costs (see Section 3). 

3. Real case-mix change equals the change in mean values times the regression coefficient for the appropriate time period. 

 

Source: Abt Associates, 2010 



2008 

 

 


