Call, K. T., B. Dowd, R. Feldman, N. Lurie, M. McBean, and M. Maciejewski. 2001. “Disenrollment from Medicare HMOs.” American Journal of Managed Care 7 (1): 37-52.

BACKGROUND: Since the program's inception, there has been great interest in determining whether beneficiaries who enter and subsequently leave Medicare health maintenance organizations (HMOs) are more or less costly than those remaining in fee-for-service (FFS) Medicare. OBJECTIVES: To examine whether relatively high-cost beneficiaries disenroll from Medicare HMOs (disenrollment bias) and whether disenrollment bias varies by Medicare HMO market characteristics. In addition, we compare rates of surgical procedures and hospitalizations for ambulatory care-sensitive conditions for disenrollees and continuing FFS beneficiaries. DESIGN: Cross-sectional analysis of 1994 Medicare data. PARTICIPANTS AND METHODS: Medicare beneficiaries were first sampled from the 124 counties with at least 1000 Medicare HMO enrollees. From this pool, HMO disenrollees and a sample of continuing FFS beneficiaries were drawn. The FFS beneficiaries were assigned dates of "pseudodisenrollment." Expenditures and inpatient service use were compared for 6 months after disenrollment or pseudodisenrollment. RESULTS: The HMO disenrollees were no more likely than the continuing FFS beneficiaries to have positive total expenditures (Part A plus Part B) or Part B expenditures in the first 6 months after disenrollment. However, disenrollees were more likely to have Part A expenditures. Among beneficiaries with spending, disenrollees had higher total and Part B expenditures than continuing FFS beneficiaries. Moreover, the disparity in total and Part B spending between disenrollees and continuing FFS beneficiaries increased with HMO market penetration. Although Part A spending was higher for disenrollees with spending, it was not sensitive to changes in market share. The HMO disenrollees received more surgical procedures and were hospitalized for more of the ambulatory care-sensitive conditions than the FFS beneficiaries. CONCLUSIONS: On several measures, Medicare HMOs experienced favorable disenrollment relative to continuing FFS beneficiaries as recently as 1994, which increased as HMO market share increased.