hold includes an AFDC/TANF unit. For Medicaid, the filing unit may be either a family or an individual.

Eligibility simulations are performed on a month-by-month basis. Thus, a family might be eligible for a program in one month but not another, or eligible for a different amount in one month than another. Note, however, that only one set of rules is stored in the database for each year. The rules used for each year are the rules in effect for the majority of that year.

For additional details about simulating eligibility for the transfer programs, see the TRIM3 web site at <trim3.urban.org>.

Modeling the Participation Decision

For each transfer program, TRIM3 determines whether a particular filing unit that is eligible for that program will in fact apply for and receive the benefits from that program. The CPS respondents do report whether the household received food stamps or TANF and whether any of the members were enrolled in Medicaid (again, these reports are on an annual basis). However, there is serious underreporting of transfer program benefits (Wheaton and Giannarelli, 2000). The public-use CPS captures only about 61 percent of the 1998 TANF caseload, 67 percent of the Food Stamp Program caseload, and 68 percent of the Medicaid caseload. The TRIM3 simulation corrects for this underreporting of transfer benefits.

Participation methodologies vary somewhat among the simulated programs, but several general methods apply to all programs. Units that are eligible for assistance and report receiving assistance on the CPS are assigned to participate. Note that responses that were “allocated” (imputed) by the Census Bureau are not considered to be actual reports. Units that are simulated to be ineligible for assistance are not assigned to participate, even if they report receiving that assistance according to the CPS data. Additional eligible nonreporters are selected to participate in such a way that the simulated caseload matches the caseload reported from administrative records as closely as possible in terms of size as well as key characteristics—typically unit type, benefit level, citizenship status, and state. Thus, the final TRIM3 version of the CPS data corrects for the under-reporting of transfer benefits.

For additional details about how TRIM3 models participation for each of the transfer programs, see the project’s web site at <trim3.urban.org>.

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