15 states where largest insurer has at least 50% of market

Fifteen states in the U.S. have a health insurer that holds at least half of the commercial market, according to an analysis from the American Medical Association. 

For the 2020 study of U.S. health insurance markets, researchers with the AMA analyzed market concentration in 384 metropolitan statistical areas, 50 states and the District of Columbia. The researchers used the Herfindahl-Hirschman Index, a commonly accepted measure of concentration used in federal antitrust cases, to analyze competitiveness.

Here are the 15 states where the largest commercial health insurer holds at least half of the market. The percentage of market share the largest insurer holds is also listed next to each state: 

1. Alabama 
Share: 86 percent

2. Michigan
Share: 67 percent

3. Hawaii 
Share: 66 percent

4. South Carolina 
Share: 64 percent

5. Delaware 
Share: 64 percent

6. Kentucky 
Share: 64 percent

7. Louisiana 
Share: 62 percent

8. Illinois 
Share: 59 percent

9. Indiana 
Share: 56 percent

10. Mississippi
Share: 55 percent

11. North Carolina 
Share: 55 percent

12. Oklahoma
Share: 55 percent

13. North Dakota 
Share: 54 percent

14. Vermont
Share: 53 percent  

15. Alaska 
Share: 51 percent

See the list here. View the 10 states with the most concentrated markets here.

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