Brian Biles and other analysts at the Commonwealth Fund have produced a set of market concentration tables for the Medicare Advantage market.

The Commonwealth Fund has a reputation for being skeptical about the role of private insurers in the U.S. health care finance system, and fund analysts developed the tables, which are based on 2012 data, for a commentary in which they argue that letting private plans enter a health care market does not necessarily lead to real competition.

The Medicare Advantage program, or Medicare Part C, is a program that lets private insurers sell replacement plans for the traditional Medicare program coverage to Medicare enrollees.

Opponents of the Medicare Advantage program and earlier private Medicare plan programs say they increase per-enrollee Medicare costs.

Supporters of the private Medicare plan programs say that making valid, apples-to-apples comparisons of per-enrollee costs is difficult; that many consumers prefer Medicare Advantage plans to traditional Medicare; and that any weaknesses in competition are the result of government red tape, not of problems with the concept of using free-market competition to improve the health care market.

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Readers on either side on the issue might find the underlying data interesting.

One table shows the market share of the top Medicare Advantage carrier in each of the 100 counties with the most Medicare Advantage plan enrollees.

In five of those counties, the top Medicare Advantage carrier covers 75 percent of the Medicare Advantage enrollees and is close to having what amounts to a private-sector single-payer system in that county.

For a look at the counties with the biggest Medicare Advantage market gorillas, read on.

5. Tarrant, Texas

Medicare Advantage enrollees: 55,692

Biggest Medicare Advantage carrier: UnitedHealth Group.

Market share of biggest Medicare Advantage carrier: 77%

 

4. Baltimore City, Md.

Medicare Advantage enrollees: 6,451

Biggest Medicare Advantage carrier: Cigna

Market share of biggest Medicare Advantage carrier: 78%

  

3. Suffolk County, N.Y.

Medicare Advantage enrollees: 37,781

Biggest Medicare Advantage carrier: Anthem

Market share of biggest Medicare Advantage carrier: 78%

 

2. Fairfax, Va.

Medicare Advantage enrollees: 2,469

Biggest Medicare Advantage carrier: Humana

Market share of biggest Medicare Advantage carrier: 79%

 

1. DuPage County, Ill.

Medicare Advantage enrollees: 3,947

Biggest Medicare Advantage carrier: Humana 

Market share of biggest Medicare Advantage carrier: 85%

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