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Suggested Citation:"Comparing Model Runs." 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 158

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FUTURE COMPUTING ENVIRONMENTS FOR MICROSIMULATION MODELING 158 this calculation would be copied to a user directory and edited using a text editor, and then it would be recompiled and a new SPSD/M executable program regenerated under the control of a supplied Makefile.14 Other types of simulation requirements that require the glass box approach are adding new parameters, new variables, or new operating characteristics. Since the developers of SPSD/M must make the above types of changes in order to support their own research efforts, the system has been designed to accept them as simply as possible. Few of the current SPSD/M users have had to make such changes though since the model has many of the recent and proposed changes built in. The information required to modify the SPSD/M source code is documented in the SPSD/M Programmer's Guide (Statistics Canada, 1990). A complete SPSD/M model run using the 1988 prereform scenario on the complete 1984 SPSD, which produces all the default tables but no custom tables, required approximately 8 minutes of elapsed time on a Compaq Deskpro 386/25 with a 25-MHz 80387 coprocessor. A more complex model run that uses the 1988 prereform scenario as the base model and the 1988 reform as a variant model and that produces marginal tax rate information for both scenarios required approximately 24 minutes of elapsed time on the same microcomputer. Comparing Model Runs SPSD/M permits two model runs to be compared in several different ways. The built-in tables permit the user to examine gross and net flows between governments and households or individuals. These tables also indicate the number of winners and losers by comparing the consumable income of individuals or families for each model run. If the built-in reporting facilities are not adequate for a user's requirements, the user can create the required variables by using the user-defined variables facility. These new variables can then be included in custom tables that can be defined using the X-Tab tabulation facility. These two features of SPSD/M can be invoked by changing a set of special parameters. Although the input language to the two facilities is somewhat cryptic, it is well documented in the SPSD/M manuals. No C language programming is necessary. If the user's analysis cannot be supported by these features, two alternatives are possible. First, the user can output the required data from the variant and base model runs and then input the two result files to another statistical package such as SAS. The other alternative is to modify the SPSD/M source code to carry out the required analysis. 14 SPSD/M development was carried out using several software engineering tools commonly used by UNIX C programmers. The UNIX Make program permits a developer to state in a Makefile a set of rules that control the recompilation and linking of the system under development. The SPSD/M package includes a public domain version of Make and the required Makefiles.

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Improving Information for Social Policy Decisions -- The Uses of Microsimulation Modeling: Volume II, Technical Papers Get This Book
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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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