found with the Phase I data, explains the effect it has on the point estimates of the size of the underestimation, and discusses the implications for the panel’s conclusions in the Phase I report.

Current methods for estimating WIC eligibility make only a minor adjustment to account for persons who are adjunctively eligible for WIC. Differences in eligibility rules between WIC and Medicaid, food stamps, and TANF make it possible for an applicant whose family income is above the WIC income eligibility threshold (185 percent of federal poverty guidelines) to be eligible for WIC because he or she participates in at least one of the other three programs. The most notable differences in eligibility rules are those between the WIC and Medicaid programs. In several states, the Medicaid program has a higher income eligibility threshold than the WIC income threshold. In addition, Medicaid uses a net income measure to determine eligibility, allowing certain deductions and income disregards, while WIC only considers gross income. These allowable deductions and disregards also make it possible for someone to have a gross income above the WIC income threshold but a net income below the Medicaid threshold.

In the Phase I report the panel examined how many additional infants and children would be eligible for WIC if estimates accounted for adjunctive eligibility. To estimate the number adjunctively eligible, the panel obtained data from the Urban Institute’s Transfer Income Microsimulation Model 3 (TRIM). Data from TRIM were used instead of the data currently used by USDA to estimate eligibility, the March Income Supplement of the Current Population Survey (CPS), because the CPS suffers from underreporting of participation in Medicaid, food stamps, and TANF. For example, the 1999 March CPS (which asks questions about a family’s income in calendar year 1998) only captured 68 percent of the Medicaid caseload, 67 percent of the food stamps caseload, and 61 percent of the TANF caseload according to 1998 administrative records from these programs (Wheaton and Giannarelli, 2000). TRIM starts with the public-use version of the CPS data, but attempts to correct for underreporting of participation in each of these programs by simulating participation.

TRIM corrects for the underreporting of Medicaid by randomly selecting persons who do not report Medicaid participation, but whose incomes and other characteristics indicate they are eligible for Medicaid. The number of eligible people randomly selected as “participants” is computed so that the total number selected matches caseload totals from administrative records for each state, by broad eligibility categories. In standard practice, TRIM simulates Medicaid participants to match average monthly control totals of participants.

For the Phase I report (National Research Council, 2001), the panel used 1998 income data from TRIM (from the 1999 March CPS) to estimate the numbers of infants and children who would be eligible for WIC if adjunctive eligibility were accounted for in estimating the number of infants and children eligible for WIC.1 Estimates of the numbers of infants and children who met income eligibility requirements for WIC were calculated using the USDA’s current methods. These “baseline” estimates were compared with estimates of infants and children who met income eligibility requirements for WIC or who were enrolled in Medicaid, food stamps, or TANF. As noted above, the panel found that accounting for adjunctive eligibility increased the number of infants eligible for WIC by 45 percent over the USDA baseline estimates and the number of children eligible for WIC by 21 percent. Based on these estimates, the panel concluded that “Not fully accounting for adjunctive eligibility results in a


The panel focused only on infants and children because estimates of the number of eligible women are derived from the estimates of eligible infants.

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