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EVALUATIONS OF MICROSIMULATION MODELS: LITERATURE REVIEW 255 7 Evaluations of Microsimulation Models: Literature Review Michael L.Cohen This chapter presents a short history of the literature on the validation of microsimulation models. The 13 sources cited, while probably not complete, comprise a large majority of the available studies on this topic.1 Given that microsimulation models have been in existence for over 20 years and that during this time at least 6 major and 10â20 minor microsimulation models have been developed,2 it is surprising that little effort has been devoted to determining the likely error present in the models. No doubt there are reports prepared for internal use that I am not aware of, but my impression is that internal reports typically focus on computer software verification or assessment of the accuracy of baseline simulations compared with outside control totals. They are almost certainly not attempts either to compare the projections from microsimulation models with the truth (i.e., to conduct an external validation) or to otherwise Michael L.Cohen is assistant professor in the School of Public Affairs at the University of Maryland; he served as a consultant to the Panel to Evaluate Microsimulation Models for Social Welfare Programs. 1After this study was essentially complete, a study by Wertheimer et al. (1986) was discovered. Although it should have been included here, its inclusion would not have qualitatively affected the conclusions. 2Examples of microsimulation models include the Urban Institute's Dynamic Simulation of Income Models (DYNASIM and DYNASIM2) and Transfer Income Models (TRIM and TRIM2), Mathematica Policy Research's Micro Analysis of Transfers to Households (MATH) model, Lewin/ICF's Household Income and Tax Simulation Model (HITSM) and Pension and Retirement Income Simulation Model (PRISM), the Multi-Regional Policy Impact Simulation (MRPIS) model, and the tax policy microsimulation model of the U.S. Treasury Department.