Selection bias and utilization of the dual eligibles in Medicare and Medicaid HMOs.

OBJECTIVE: To examine the existence of selection bias in the first 3 years of the Minnesota Senior Health Options (MSHO) demonstration and to estimate the MSHO effects on medical services utilization after adjusting for selection bias. DATA SOURCES: Monthly dual eligibility data and MSHO encounter data of March 1997-December 2000 and Medicaid encounter data of January 1995-December 2000 from the Minnesota Department of Human Services; Medicare fee-for-service claims data of January 1995-December 2000 from the Centers for Medicare and Medicaid Services. STUDY
DESIGN: Quasi-experimental design comparing utilization between MSHO and control groups; multiple econometric and statistical models were estimated with time-invariant and time-varying covariates. PRINCIPAL
FINDINGS: Favorable MSHO selection was found in the nursing home (NH) and community populations, but selection bias did not substantially affect the findings. Enrollment in MSHO for more than 1 year reduced inpatient hospital admissions and days, emergency room and physician visits for NH residents, and lowered physician visits for community residents.
CONCLUSIONS: There was favorable selection in the first 3 years of the MSHO program. Enrollment in MSHO reduced several types of utilization for the NH group and physician visits for community enrollees. © Health Research and Educational Trust.