Report to Congress: Medicare Beneficiary Enrollment by Congressional District and State
May 2017
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, 2016.
	    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 in the TIGER/Line Shapefiles provided by the Census Bureau. About nine percent of beneficiaries were not geocoded to a precise location because their address was a post office 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 level and beneficiaries are counted by the characteristics shown in each table.

Geocoding Results	
	    - 92.0 percent of Medicare beneficiaries were geocoded to their exact location.
	    - 7.2 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 239 records were unable to be geocoded due to invalid information.
 
Status	Beneficiary Count	Percent of Total (%)	   
Geocoded at a precise location	52,314,894	92.0	   
Geocoded at the zip code level based on the population patterns of each zip code	4,092,355	7.2	 
Not located within the U.S.	476,532	0.8	   
Invalid data - Unable to geocode	239	0.0	   
Total	56,884,020	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 August 19, 2016. Legal boundaries and names are up to date, as of January 1, 2016.
    - Previous years' totals should be compared using the same pull date as the current analysis.
    - 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 2016.  
    - Total Medicare Advantage (MA) enrollment as a % 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 22,000 Medicare eligible beneficaries 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.



