Adverse selection and the purchase of Medigap insurance by the elderly.

This study uses data on 8561 elderly respondents from the 1991 Medicare Current Beneficiary Survey to examine adverse selection in the supplemental private insurance market. Logit models of supplemental insurance choices provided modest but mixed evidence of self-selection on the basis of observable health status. Wealth had a strong influence on coverage. Two part models of Medicare utilization and expenditures showed that beneficiaries with individually purchased policies had higher total, part B and physician expenditures than those with employer-provided policies, even after controlling for observable differences, suggesting adverse selection. Results were similar for basic and more comprehensive policies.