Health care use and expenditures of Medicare HMO disenrollees.

We examine the impact of the first wave of Medicare health maintenance organization HMO withdrawals. With data from CMS and United Health Group, we estimate use and expenditure changes between 1998 and 1999 for HMO enrollees who were involuntarily dropped from their plan and returned to fee-for-service (FFS) Medicare using a difference-in-difference model. Compared to those who voluntarily left an HMO, involuntarily disenrolled beneficiaries had higher out-of-pocket expenditures, an 80 percent decrease in physician visits, 38 percent higher emergency room (ER) use and a higher probability of dying. The results suggest beneficiaries face significant costs and reduced health outcomes from unstable Medicare managed care markets.