HMO enrollment: who joins what and why: a review of the literature.

Enrollment in an HMO involves a simultaneous choice of insurance benefits and a provider system. Review of an extensive series of studies shows that breadth of coverage, lower cost, and assured access to benefits are key elements anticipated in the choice. But so too are the perceived limitations inherent in selection of a physician within a close-panel plan, and the inconvenience of centralized sites. For the design and evaluation of future policy, current knowledge based on past enrollment behavior offers only tentative suggestions.