In our research with SIPP data we found that 18 percent of the children we simulated to be eligible for Medicaid reported having some form of insurance coverage other than Medicaid (Czajka 1999). This other coverage could represent Medicaid being misreported as something else, or it could represent genuinely different coverage. In the former case, there are clear implications for the calculation of Medicaid participation rates. Indeed the misreported coverage would account for part of the Medicaid undercount. If there were a way to resolve this with the survey data and determine how many of the children who reported other coverage may have actually been covered by Medicaid, then the quality of a survey-based participation rate could be improved. To the extent that it is not possible to discern the amount of misreporting and in so doing correct the survey data, the argument for considering administrative data for the numerator is strengthened.
The possibility that much if not most of the reported other coverage is truly something other than Medicaid suggests another strategy--perhaps one that is best viewed as a complementary strategy rather than an alternative one. Nonparticipation in Medicaid by eligible children who have other coverage carries very different policy implications than nonparticipation by those who are uninsured. Medicaid participation rates calculated for just those children who would otherwise be uninsured may provide a more meaningful indication of the success of Medicaid outreach than participation rates that count eligible children with other coverage as eligible but not participating. Even without adjusting for Medicaid underreporting, we found that the participation rate among eligible children with no other coverage was 79 percent, compared with 65 percent for all eligible children (Czajka 1999).