Factors affecting interstate use of inpatient care by Medicare beneficiaries.

This article examines the extent to which interstate inflow and outflow of patients affects their observed use of Medicare Part A inpatient care. Interstate patient flow can bias utilization rates and may be due to seasonal migration, interstate inpatient care market areas, or purposive seeking of specialized/high-quality care. Examination of state level patient flow data drawn from 1987 Medicare discharge indicate that most interstate patient flow occurs between adjacent states probably as an outgrowth of interstate markets. Regression analyses of patient flow data suggest that while seasonal migration is an important determinant of patient flow, its importance is secondary to that of indicators of the availability of specialized services. These findings suggest research questions that may be best answered in detailed analyses of inpatient utilization in interstate market areas and seasonal migration.