Health maintenance organizations' (HMOs) restrictions on the size of their physician networks have raised concerns that individuals who switch health plans or jobs (which usually involves changing health plans) may have to leave preferred physicians. A new study provides the first national estimate of the extent to which restricted networks actually limit a person's access to physicians. The researchers calculated that people who switch HMOs have a reasonable likelihood (50 percent chance) of being able to retain their physician.
Investigators supported by the Agency for Healthcare Research and Quality (HS10771) used data from electronic HMO provider lists of more than 500,000 physicians and 6,000 hospitals to quantify the extent of provider overlap (the probability that a physician in any given plan is also in a competing plan) in U.S. metropolitan markets. The national measure of overlap is 0.48, indicating that the probability that a given HMO enrollee's physician is also in a competing HMO is 48 percent, or about half.
Overlap varies with both plan and market attributes. Not surprisingly, group/staff-model plans have virtually no overlap, since their providers are all part of the health plan staff. Other plan types have high levels of overlap, while younger plans, for-profit plans, and plans in small markets have greater overlap. The Mid-Atlantic and New England regions have higher managed care penetration and higher overlap, while the Southern region has less penetration and only moderate overlap. In contrast, the Western region is home to the oldest HMO plans, many of which are group/staff models that have virtually no overlap with other plans.
See "Overlap in HMO physician networks," by Michael E. Chernew, Ph.D., Walter P. Wodchis, Ph.D., Dennis P. Scanlon, Ph.D., and Catherine G. McLaughlin, Ph.D., in the March 2004 Health Affairs 23(2), pp. 91-101.
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