THE METHODOLOGY PRESENTED IS BASED UPON A SIMULATION MODEL CALLED THE SIMULATED LOSSES/ADMISSIONS MODEL, DEVELOPED BY THE STAFF OF THE BUREAU OF PLANNING, RESEARCH, AND STATISTICS. THE MODEL WAS DEVELOPED TO PREDICT THE PROBABLE DATE OF RELEASE FOR EACH INDIVIDUAL IN CUSTODY AS WELL AS FOR THOSE ADMITTED TO DEPARTMENT OF REHABILITATION INSTITUTIONS, THEREBY PREDICTING FUTURE LEVELS OF INMATE POPULATION. PHASE I DEVELOPMENT OF THE MODEL IS PRESENTED IN THIS REPORT. EFFORTS IN THIS PHASE WERE DIRECTED PRIMARILY TOWARD UNDERSTANDING THE DYNAMICS OF THE CORRECTIONAL SYSTEM AND TO PROVIDING AN ANALYSIS OF FACTORS CONTRIBUTING TO THE GROWTH OR DECLINE AND DEMOGRAPHIC CHARACTERISTICS OF THE INMATE POPULATION. IN ORDER TO DEVELOP THE 3-YEAR AND 23-YEAR ESTIMATES OF INMATE POPULATIONS PRESENTED, IT WAS NECESSARY TO BASE THE MODEL ON PREDICTED ADMISSIONS FROM A MULTIPLE REGRESSION ANALYSIS ON FACTORS CONSIDERED APPROPRIATE. THESE FACTORS ARE STATE POPULATION AND POPULATION OF MALES AGES 18-29 POPULATION AT RISK AND PREDICTABLE ECONOMIC CONDITIONS LIKELY TO AFFECT THE CRIMINALITY OF THE POPULATION AT RISK. THE MODEL CONSIDERS THE DISTRIBUTION OF THE ACTUAL TIME SERVED FOR THOSE WHO HAVE BEEN RELEASED, ADJUSTS THIS DISTRIBUTION TO ACCOUNT FOR THE TIME SERVED BY PERSONS WHO HAVE NOT YET BEEN RELEASED, AND PREDICTS A PROBABLE RELEASE DATE FOR EVERY OFFENDER. IN THE DESIGN OF THE MODEL, CONSIDERATION WAS GIVEN TO CRIMINAL LAW PENALTIES AND ADMINISTRATIVELY CONTROLLED VARIABLES SUCH AS A VARYING NUMBER OF RELEASE DAYS IN A GIVEN MONTH IF THE END OF THAT MONTH FALLS ON A WEEKEND OR HOLIDAY. A RIGOROUS TESTING OF THE MODEL WAS CONDUCTED THAT INCLUDED COMPARISON OF MONTH-TO-MONTH PROJECTIONS WITH THE ACTUAL END-OF-MONTH POPULATION, BEGINNING WITH THE STATUS POPULATION OF JUNE 30, 1973. IN THIS CASE THE MODEL WAS BASED ONLY ON GROSS ANNUAL ADMISSIONS FOR THE FOLLOWING 4 YEARS. RESULTS OF THE TESTING ARE REPORTED. TABULAR AND GRAPHIC DATA ARE PROVIDED. (AUTHOR ABSTRACT MODIFIED-RCB)