The AMA recently released a special analyses of commercial health insurance markets that found the "combined impact of proposed mergers among four of the nation's largest health insurance companies would exceed federal antitrust guidelines designed to preserve competition in as many as 97 metropolitan areas within 17 states," and that "all told, the two mergers would diminish competition in up to 154 metropolitan areas within 23 states."

Two healthsprocket lists have just been posted from their analyses:
The 10 states with the least competitive commercial health insurance markets
The 10 states that experienced the biggest drop in health plan competition levels between 2010 and 2013

The AMA study found that:
- In nearly two out of five metropolitan areas studied, a single health insurer had at least a 50 percent share of the commercial health insurance market.
- 14 states had a single health insurer with at least a 50% share of the commercial health insurance market.
- 46 states had two health insurers with at least a 50%t share of the commercial health insurance market