Response error and the Medicaid undercount in the current population survey.

Objective To measure the Medicaid undercount and analyze response error in the 2007-2011 Current Population Survey Annual Social and Economic Supplement (CPS ASEC). Data Sources/Study Setting Medicaid Statistical Information System (MSIS) 2006-2010 enrollment data linked to the 2007-2011 CPS ASEC person records. Study Design By linking individuals across datasets, we analyze false-negative error and false-positive error in reports of Medicaid enrollment. We use regression analysis to identify factors associated with response error in the 2011 CPS ASEC. Principal Findings We find that the Medicaid undercount in the CPS ASEC ranged between 22 and 31% from 2007 to 2011. In 2011, the false-negative rate was 40%, and 27% of Medicaid reports in CPS ASEC were false positives. False-negative error is associated with the duration of enrollment in Medicaid, enrollment in Medicare and private insurance, and Medicaid enrollment in the survey year. False-positive error is associated with enrollment in Medicare and shared Medicaid coverage in the household. Conclusions Survey estimates of Medicaid enrollment and estimates of the uninsured population are affected by both false-positive response error and false-negative response error, and these response errors are non-random.