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DOCUMENTATION FOR MICROSIMULATION MODELS: A REVIEW OF TRIM2, MATH, AND HITSM 344 or a tutorial on how to run the model for parametric applications. Analysts are sufficiently computer literate that they could learn something about how the model operates by seeing sample run set-ups and printouts, even if they will never apply the model themselves. Furthermore, the instructional material should relate the Technical Description to the User's Guide. Besides an instructional chapter, the Technical Description would benefit from mechanisms to make it more user friendly. A table of contents for each section should be added. Obsolete material should be deleted. The use of formulas with unexplained mnemonics for very simple recodes of variables should be eliminated. Lengthy tables of parameters could be put in appendixes. The MATH User's Guide, on the other hand, is fairly user friendly except for its virtual omission of preliminary materials and pagination. An introduction should be added that explains the organization of the document, how it relates to the MATH Technical Description, the archiving scheme, the conventions used in the text, and so forth. HITSM The HITSM documentation (Lewin/ICF, Inc., 1988) and, if the documentation accurately reflects the model, the model are quite distinct from TRIM2 and MATH. The HITSM documentation consists of a single report that documents a study in which a reasonably broad measure of household disposable income was estimated for all the observations on a microdata file. The report has chapters on the creation of the database, aging the database, imputation of public assistance, and imputation of taxes. On the basis of this document, one could easily quibble about whether HITSM is a model. The document never discusses user parameters, inputs, options, or outputs. Rather the style of the document is to describe how Lewin/ICF, Inc., estimated disposable income on a microdata basis and to validate the estimates by comparing aggregated microdata to outside sources. In fact, the document often says âthis studyâ or âthis analysisâ instead of âthe modelâ (see pp. II-3, II-15, II-38, and III-5). Critique On the positive side, the document does attempt to address the accuracy of the model's output. In the documentation for MATH and TRIM2, validation or model accuracy is never addressed. Also, the HITSM documentation provides many references to external data sources or studies and thus provides the reader with a sense that ICF has carefully grounded its work in prior literature. On the negative side, the document is comparable to the other documents the panel reviewed in terms of typographical errors, inconsistent formatting, and lack of clarity. Particularly disturbing about the HITSM document is that factual errors are present in the content Page II-2 states: âThe CPS is a