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.