Total HMO enrollment in metropolitan statistical areas (MSAs) in a recent InterStudy market analysis ranges from one enrollee in Victoria, Texas, to more than 5.4 million in Los Angeles-Long Beach, Calif. The study found that almost three quarters (74.2 percent) of the 72.3 million HMO members in metropolitan areas are in large markets (1 million or more enrollees).
Large markets tend to be more competitive than smaller markets as measured by the study's Index of Competition. Values range from 0, a monopoly, to 1, competition among many HMOs with similar market shares. Among medium-sized markets (250,000–999,999 enrollees), Lakeland-Winter Haven, Fla., has the highest IOC (0.900). Merced, Calif., is the most highly competitive small market (fewer than 250,000 enrollees) with an IOC of 0.834.