The impact of HMOs: evidence and research issues.

This paper reviews the evidence concerning the impact of HMO growth on traditional providers. Primary emphasis is placed on the results of three case studies conducted by the author. Based on the case studies, five factors are hypothesized to be important in determining the extent of HMO impact on a community: employer attitudes, hospital capacity, physician supply, planning and regulatory decisions, and comprehensiveness of health benefit coverage. Since research on this general topic is in its infancy, several important questions deserving future research effort also are identified.