Medicare Advantage and the impact of Medicare HMOs on inpatient utilization.

(1) Health maintenance organizations (HMOs) decrease inpatient utilization for Medicare enrollees. (2) California group and staff HMO enrollees used 18 percent fewer inpatient days than had they continued in Medicare fee-for-service (FFS) plans, with an 11 percent reduction for independent practice association (IPA) HMO enrollees.