Abstract
Growth in the size and power of managed care organizations is widely thought capable of transforming fundamentally the structure and functioning of the entire health care system. Not only can health maintenance organizations (HMOs) and other managed care organizations influence the care provided to the patients that they cover, but also the activities of these organizations may bring about broad, system-level changes in the delivery of health care. Such "spillover effects" of managed care could ultimately affect even patients who have not joined managed care organizations. This study investigates the relationship between managed care activity and health care for patients not enrolled in managed care organizations.