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Administration for Community Living 

Tip Sheet 

Medicare Advantage Plan Market Share Analysis 

Top Five Plans by County 

Purpose: 

The Centers for Medicare & Medicaid Services (CMS) provides monthly data on 

Medicare Advantage enrollment in the United States, by County. This tip sheet 

provides an overview on how to conduct a market analysis to determine the top 

Medicare Advantage plans, by enrollment in a specific county. 

Background: 

Medicare Advantage, also known as Medicare Part C, provides an option for 

Medicare beneficiaries to enroll in a managed care plan to administer their Medicare 

benefits. Medicare Advantage (MA) plans have different levels of market share 

depending on the specific market. If a community-based organization (CBO) wishes 

to provide reimbursable services to a beneficiary who is enrolled in an MA plan, 

then the organization must contract directly with the MA plan before initiating 

services for the target population. 

Procedure: 

1. First, access the CMS website dedicated to providing Medicare Advantage 

plan and Medicare Part D enrollment using the following link: 

https://www.cms.gov/MCRAdvPartDEnrolData/01_Overview.asp#TopOfPage

The following screenshot shows the CMS webpage that is accessed using the link 

above: 
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2. Once at the webpage, you will see a series of options along the left side of the 

page. In order to determine the Medicare Advantage Penetration numbers 

in the requested County, you will access the following table: 

Monthly_MA_Enrollment_by_State/County/Contract 

3. When you click on that link, you will see a listing of available files, in 

chronological order using based on date (YYYY-MM): 
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4. Identify the month for which you would like to view the MA plan enrollment 

data, and click on that file. 

5. When you click you will be prompted to download a CSV File. When 

prompted, accept the request to download the requested file. NOTE: Choose 

the “Abridged” file to filter out any plan with fewer than ten (10) enrollees. 

6. Open the downloaded file 

7. When you open the downloaded file, you will note that it is a large file and 

that the data is categorized in alphabetical order by county and then by state. 

8. Scroll to the state and county that you wish to analyze 
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9. Scroll across the table to determine the key data elements for the market you 

are analyzing. When you identify the reference county, sort the list by the 

Enrolled column (the number of persons enrolled in each MA plan). 

 Example: 

The process for sorting and analyzing MA Plan enrollment by county is as 

follows: 

a. Sort the data using the following commands. 

i. Select “Data” from the Menu bar

ii. On the Data drop down menu, select “Sort”
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b. Once you have selected the Sort command, you will have an option to 

“Customize” your Sort using the following selections

c. Using the Sort Commands, you can customize the presentation of the data 

by State, then by County, then by health plan enrollment numbers, using 

the following selections: 

i. Select Sort by State 

ii. Select Sort by County 

iii. Select Sort by Enrollment – Largest to Smallest 
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Select additional sort fields by clicking on the “Plus” (+) symbol

Once the list is sorted by State, by County, and then by enrollment, scroll to 

the appropriate County and assess the plans by enrollment number rankings. 

Select Largest to Smallest 
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For example, in Dallas County, TX (September 2014): Top Five MA Plans by 

Enrollment 

1. United Healthcare Benefits of Texas, Inc. (HMO): 41,273 

2. Aetna Life Insurance Company (PPO): 7,120 

3. Wellcare of Texas, Inc. (HMO): 5,108

4. Aetna Health, Inc. (HMO): 5,004 

5. Humana Health Plan of Texas, Inc. (HMO): 4,899
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Utility of the Data:

This enrollment data provides insight into which MA plan has the largest market 

share in a particular county. This data can help a CBO develop a contracting 

strategy for their particular market. In the Dallas, TX example, the local CBO could 

place their focus on working with United Health Care MA plan because they have the 

overwhelming majority of the local market share.