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DYNASIM2 AND PRISM: EXAMPLES OF DYNAMIC MODELING 121 4 DYNASIM2 and PRISM: Examples of Dynamic Modeling Christine M.Ross THE MODELS The original dynamic simulation model, the Urban Institute's Dynamic Simulation of Income Model (DYNASIM), was developed between 1969 and 1976 by Guy Orcutt, Steven Caldwell, Richard Wertheimer, and others. The model was designed to simulate demographic changes and the income of individuals and families for a variety of policy purposes. The model began with a cross-sectional database of individuals and families and simulated demographic and economic events for each individual. Individuals were married or divorced; children were born and received education; adults obtained jobs, received earnings, retired, and died. Simulations were based on a model of each event, which ranged from simple (the probability of the event depends on age, sex, and race) to complex (labor force participation, hours worked, and the wage received are jointly determined by an economic model). DYNASIM was updated in 1983 (and renamed DYNASIM2) to improve its ability to forecast retirement income and the effects of government policy on retirement income into the future. At that time, many of the modules governing demographic and labor force events and retirement benefits were updated or Christine M.Ross is on the staff of Mathematica Policy Research, Inc.; she served as research associate of the Panel to Evaluate Microsimulation Models for Social Welfare Programs. The author would like to thank Linda Giannarelli, Michael Wolfson, and Sheila Zedlewski for helpful comments on a previous draft.