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TRIM3 is a descendent of the first microsimulation model ever developed: the Reforms in Income Maintenance (RIM) model, first developed in 1969. The first Transfer Income Model (TRIM) was operational in 1973, and the second generation of TRIM--TRIM2--was introduced in 1980. TRIM3, which allows public access over the Internet, has been used since 1997.

RIM was designed in 1969 by members of the President's Commission on Income Maintenance Programs. The commission originally used RIM to simulate universal income-conditioned transfer programs that were being considered as alternatives to the existing welfare programs. In 1970 and 1971, RIM was expanded to simulate the administration's Family Assistance Plan, other welfare reform plans, and proposals relating to food stamp benefits, medical insurance, and day care. These developments were made at the Urban Institute under contract with the U.S. Office of Economic Opportunity (OEO), with programming and computing responsibilities handled by the Hendrickson Corporation. RIM was able to use either a CPS file or the 1967 Survey of Economic Opportunity (SEO) file as input.

The development of TRIM was funded primarily by the Urban Institute, with additional funding coming from the OEO and from the Office of the Assistant Secretary for Planning and Evaluation (ASPE), then in the U.S. Department of Health, Education, and Welfare. New aspects of the TRIM design included a flexible modular structure, extensive parameterization, self-documenting simulation runs, and an emphasis on structured programming techniques. TRIM retained the RIM concept of converting survey files to a standard input format. The new model was programmed by staff of the Hendrickson Corporation, and was operational in 1973. With continued funding from ASPE, the Urban Institute continued to use and develop TRIM throughout the 1970s.

In the mid-1970s, other organizations began to use TRIM. For example, the U.S. Treasury Department began using its own version of TRIM to supplement its in-house tax model. In addition, Mathematica Policy Research (MPR) adopted TRIM and began to add its own developments to the model. MPR named its version the Micro Analysis of Transfers to Households (MATH) model. MATH is still being used and developed by MPR today.

In 1978, HHS/ASPE funded the development of the second generation of the TRIM model. Many features of the first-generation TRIM model were retained in concept, but were implemented more comprehensively in TRIM2. The TRIM2 development effort was completed in 1980. Other support for TRIM2 came from the Congressional Budget Office, the U.S. Department of Labor, and private foundations.

In 1995, HHS/ASPE began funding the development of TRIM3. This latest version of TRIM grounds the simulation model on a computational platform that takes advantage of relatively recent advances in information technology. All parts of the model are accessible through a single, intuitive WWW interface. The simulation model is written in object-oriented C++, and data and program rules are stored in an ODBC-compliant database. TRIM3 was introduced in 1997.

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