National Academies Press: OpenBook
Suggested Citation:"HITSM." National Research Council. 1991. Improving Information for Social Policy Decisions -- The Uses of Microsimulation Modeling: Volume II, Technical Papers. Washington, DC: The National Academies Press. doi: 10.17226/1853.
Page 92

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ALTERNATIVE MODEL DESIGNS: PROGRAM PARTICIPATION FUNCTIONS AND THE ALLOCATION OF ANNUAL TO 92 MONTHLY VALUES IN TRIM2, MATH, AND HITSM 1 from the age reported by each person in March, but none of the models “grows” people during the income year or otherwise alters family composition. Location of the Annual to Monthly Conve rsion in the Model Run Stream TRIM2 The MONTHS routine, which performs the annual to monthly income conversion, is run after all other steps have been carried out to process the input data and before any of the program simulation modules are run. MATH The ALLOY routine, which performs the annual to monthly income conversion, ideally would follow all the steps to process the input data and precede all of the program simulation routines. However, in the current version of MATH, the PBLAST routine for simulating AFDC, SSI, and general assistance (GA) precedes ALLOY. This is because resource constraints have precluded modifying PBLAST to operate on monthly data. PBLAST uses a more ad hoc procedure for allocating employment status (and hence earnings) and unearned income throughout the year. ALLOY, which was implemented in 1984 and incorporates empirical evidence from the ISDP about patterns of employment and income receipt over the year, contains some code to treat AFDC- participating units consistently with the assumptions used in PBLAST. ALLOY also allocates the simulated AFDC benefits produced by PBLAST to months for subsequent use by the FSTAMP (food stamp program) routine. HITSM Conversion of annual to monthly income in HITSM takes place after all the steps to process the input data have been performed, including correction of March CPS income values for underreporting. The conversion also takes place after determination of family asset amounts but before determination of eligibility or participation in transfer programs. (HITSM, in contrast to TRIM2 and MATH, was designed as an integrated rather than a modular system. Hence, portions of program code that perform functions such as simulating particular programs are not organized into separate modules that can be invoked or not as the user determines.)

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This volume, second in the series, provides essential background material for policy analysts, researchers, statisticians, and others interested in the application of microsimulation techniques to develop estimates of the costs and population impacts of proposed changes in government policies ranging from welfare to retirement income to health care to taxes.

The material spans data inputs to models, design and computer implementation of models, validation of model outputs, and model documentation.

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