A GROUP OF LOS ANGELES COUNTY PROBATION DEPARTMENT OFFICERS WAS SELECTED FOR THIS STUDY, AND THEIR CASELOADS INVOLVED THE MOST HARD-CORE JUVENILES SERVED BY THE DEPARTMENT. THE OFFICERS REVIEWED 80 RANDOMLY SELECTED, CLOSED CASES. MOST OF THE 20 VARIABLES USED IN THE CASE SUMMARIES WERE SUSPECTED PREDICTORS OF RECIDIVISM. THE FOLLOWING QUESTIONS WERE CENTRAL TO THE INVESTIGATION: ON WHAT BASIS DOES THE OFFICER DECIDE HOW LIKELY HIS CLIENT IS TO SUCCEED DURING HIS INCOMMUNITY PROBATION PERIOD; HOW DOES THE OFFICER'S PREDICTION CORRESPOND TO STATISTICAL PREDICTIONS; HOW DO THE PREDICTIONS RELATE TO CASE PLANS FOR CLIENTS; ARE SOME CLIENT TYPES MORE PREDICTABLE; AND DO PREDICTIONS AND PLANS AFFECT THE OFFICER'S EFFECTIVENESS. PREDICTIONS WERE SUBJECTED TO A 'LENS MODEL' AND RELATIVE WEIGHT ANALYSIS. THE FIRST ANALYSIS SHOWED THAT NOT ONE OF THE OFFICERS WAS ABLE TO EFFECTIVELY USE ECOLOGICALLY VALID NONLINEAR VARIANCE IN HIS PREDICTIONS. THE MOST ACCURATE JUDGES RELIED HEAVILY ON THE FEWEST NUMBER OF CASE SUMMARY VARIABLES, WERE MOST LINEAR IN THEIR JUDGMENTS, AND WERE BEST AT WEIGHING THE THREE MOST VALID PREDICTORS. IT WAS CONCLUDED THAT LINEAR PREDICTION MODELS ARE PREFERRABLE. THE RELATIVE WEIGHT ANALYSIS, WHICH COMPARED EACH OFFICER WEIGHING VARIABLES TO ECOLOGICAL PATTERNS AND THE OFFICER CONCEPT OF HIS WEIGHT VARIABLE, REVEALED THAT OFFICERS WERE FAR MORE CONFIDENT IN PREDICTIONS OF FAILURE THAN OF SUCCESS. OFFICERS TENDING TO PREDICT FAILURE WERE LESS ABLE TO GAUGE THE PROBABILITY OF BEING CORRECT, AND THOSE WHO WERE AWARE OF THE BASE RATE FOR CLIENT OUTCOMES WERE MORE LIKELY TO PREDICT SUCCESS. APPROPRIATENESS OF CONFIDENCE AND PREDICTIVE ACCURACY WERE SIGNIFICANTLY CORRELATED WITH THE OFFICERS' SUCCESS RATES WITH THEIR CLOSED CASES. FOR CASES PREDICTED TO FAIL, MORE EMPHASIS WAS PLACED ON OUTSIDE AGENCIES FOR SUPPORT, AND LESS PLACED ON INTERPERSONAL AND INTRAPERSONAL DEVELOPMENT GOALS. SUPERVISORS' RATINGS SHOWED LITTLE INTERJUDGE AGREEMENT, AND APPEARED TO BE DETERMINED BY THE DEGREE TO WHICH THEIR PROFESSIONAL ORIENTATION MATCHED THE PERCEIVED ORIENTATION OF CASE PLANS. APPENDIXES CONTAIN PREDICTION RESPONSE WORKSHEETS, QUESTIONNAIRES, CASE SUMMARIES, AND OFFICERS' INSTRUCTIONS. REFERENCES ARE PROVIDED. (AUTHOR ABSTRACT MODIFIED)