Biased selection under the senior health plan prior use capitation formula.

A widely acknowledged shortcoming of the current AAPCC capitation formula for Medicare HMOs is its inability to adjust capitation levels for differences in health status among enrolled groups. Prior use models have been proposed as one alternative to the current AAPCC risk classes. From 1984 through 1987, Senior Health Plan (SHP) participated in a HCFA-sponsored demonstration project in which capitation payments were determined by a prior use formula incorporating information on inpatient hospital days and Part B deductibles. This paper contains findings about selection bias in SHP enrollment from analyses of preenrollment reimbursements and postenrollment mortality rates of SHP enrollees compared with Medicare FFS beneficiaries and enrollees of other Medicare HMOs in the Minneapolis-St. Paul area.