Managed care in the United States: promises, evidence to date and future directions.

In the United States, health maintenance organizations (HMOs) and preferred provider organizations (PPOs) have proliferated during the past decade. To a great extent, their growth has been based on the perceived promise of these organizations to reduce health care costs without compromising quality of care and introduce a level of competition into the health care market that would result in a more efficient and effective health care system. This paper examines the promise of managed care as delivered through HMOs and PPOs, the evidence to date on the extent to which their promise has been met, and recent developments in the organization of managed care systems.