Report to Congress: Medicare Beneficiary Enrollment by
Congressional District and State								
February 2019									
Overview and Assumptions								
									
Methodology 								
To produce the results contained in this file, the following approach was used:								
    1. Beneficiary address data were extracted from the Centers for Medicare and Medicaid Services' (CMS') Integrated Data Repository (IDR). Data included street address, city, state, and 9-digit zip code. The data were pulled as of July 1, 2018.						
    2. Using address data, beneficiaries were geocoded and assigned a latitude and longitude coordinate.							
    3. The coordinate was then used to assign a congressional district by performing a lookup with the TIGER/Line Shapefiles provided by the Census Bureau. About seven percent of beneficiaries were not geocoded to a precise location because their address was a PO box or the data was otherwise unusable. In these cases, beneficiaries were geocoded at the zip code level based on the population patterns of each zip code.							
    4. Once a congressional district was assigned for each beneficiary, the data were summarized at the congressional district level and beneficiaries were counted by the characteristics shown in each table.							
									
Geocoding Results								
    - 92.4 percent of Medicare beneficiaries were geocoded to their exact location.							
    - 6.8 percent were geocoded at the zip code level based on the population patterns of each zip code.							
    - 0.8 percent of beneficiaries had an address that was located outside of the United States.							
    - Only 11,729 out of 59,774,474 records were excluded due to invalid geographic information.							
									
Status	Beneficiary Count	Percent of Total (%)				
Geocoded at a precise location	55,210,372	92.4				
Geocoded at the zip code level based on the population patterns of each zip code	4,056,687	6.8				
Not assignable to a Congressional District	237	0.0				
Not located within the U.S.	495,449	0.8				
Invalid data - Unable to geocode	11,729	0.0				
Total	59,774,474	100.0				
									
Notes								
    - Beneficiaries residing in the U.S., Puerto Rico, and the U.S. Virgin Islands are included in this report. Due to data limitations, beneficiaries residing in other territories are excluded from this report.							
    - TIGER/Line Shapefiles were updated on September 28, 2017. Legal boundaries and names are up to date, as of January 1, 2017.							
    - Previous year's totals should be compared using the same pull date as the current analysis, which is July 1, 2018.							
    - Beneficiary enrollment totals by plan type can change between years due to adjustments in the market and plan availability. This report reflects enrollment in the Medicare market during contract year 2018.  							
    - Total Medicare Advantage (MA) enrollment as a percent of Medicare Eligible values may differ from other reports based on the timing of data collection, inclusion criteria, and type of Medicare eligibility used.							
    - Nationwide, about 16,000 Medicare eligible beneficiaries are enrolled in a Medicare Advantage plan and, within that plan, participate in a state demonstration. Although CMS IDR reports the coverage status for the beneficiaries as being in a demonstration, to better align with other CMS enrollment extracts this report totals beneficiaries by their contract type.							
