Previous studies show that survey-based reports of Medicaid participation are measured with error, but no prior study has examined measurement error in an important segment of the Medicaid population-low-income adults enrolled in Medicare. Using the Medicare Current Beneficiary Survey, we examine whether respondent self-reports of Medicaid enrollment match administrative records and present several key findings. First, among low-income Medicare beneficiaries, the false negative rate is 11.5% when the self-report is interpreted as full Medicaid and 3.7% when the self-report is interpreted as full or partial Medicaid. Second, the likelihood of a false negative report is systematically associated with respondent traits. Third, systematic measurement error results in biased coefficient estimates in models of Medicaid participation defined from self-reports, and the bias is more significant when the researcher interprets self-reports as full Medicaid coverage only. Researchers should use caution when interpreting survey reports as pertaining to full Medicaid coverage only.
Keywords: Medicaid participation; administrative data; dual eligibles; measurement error; survey data.