The data input files can be manipulated to test alternative assumptions or to update the forecast. Altering input files allows decisionmakers and analysts to determine the impact of changes on the State population's age and sex structure, the prison population's size and characteristics, and judicial decisions. Subpopulations consist of persons in prison on the day prior to the first month of the forecast, new admissions from the courts, and two subclasses of parole failures. The model is based on demographic techniques of measuring population change--adding the net arrivals to and departures from prison in each future period to the prior prison population. Length of stay and number of admissions are important in determining population size. The model is cyclical in that once a person is released from prison and readmitted, the person can serve a new sentence, be released, and again return to prison. The cycle can continue throughout the 15 years of the forecast. Anyone released from prison has approximately a 30 percent chance of returning within a 5-year period. For each program, the report includes data input matrices, program flow charts, and the FORTRAN program. It includes six detailed examples of how to update or test alternative forecasts.