Toward new typologies for HMOs.

The evolution of health maintenance organizations (HMOs) has entailed changes in both their structural characteristics and incentives to attract physicians' participation. Previous classifications of HMOs have failed to capture explicitly key features of these changes. Two alternative typologies based on incentives or organizational structures may be constructed by examining precise forms of two- or three-tiered contractual arrangements, physicians' payment methods, clienteles served, and means of pooling risks. Classifications of these kinds may represent or aid in generating a valid typology to help managers, consumers, providers, and analysts understand better how HMOs operate and which factors are critical in the dynamic managed-care industry.