A STUDY OF DATA ON JUVENILE OFFENDERS FROM THE PHILADELPHIA POLICE SHOWS NOT ONLY THE EVOLUTION OF A SYSTEM OF RECORDING 'CONTACTS,' BUT ALSO HOW UNUSUAL VARIATIONS OR IRREGULARITIES APPEAR IN THE HANDLING OF CASES AND HOW THE DECISION TO MAKE A RECORD OF CONTACTS OR TO ARREST CHILDREN CAN CHANGE FROM YEAR TO YEAR. FOR INSTANCE, IN PHILADELPHIA, OF THOSE ON WHOM A RECORD IS MADE, BOYS MORE OFTEN THAN GIRLS, AND BLACKS MORE FREQUENTLY THAN WHITE, WIND UP IN THE ARREST GROUP. AND, NOT UNEXPECTEDLY, THE ARREST RATE IS FOUND TO VARY BY OFFENSE, WITH THE CLASS OF SERIOUS OFFENSES MORE LIABLE TO ARREST THAN THE JUVENILE STATUS OR MINOR OFFENSES. EVIDENCE AVAILABLE ON POLICE DISPOSITIONS IN OTHER PLACES CONCURS WITH THE PHILADELPHIA FINDINGS. AT THIS STAGE OF THE INQUIRY, HOWEVER, ADDITIONAL DIMENSIONS NEED TO BE DETERMINED FOR THE POLICE DISPOSITION PROCESS IN ALL PARTS OF THE COUNTRY BEFORE SOCIOLOGICALLY SOUND EXPLANATIONS CAN BE EMBARKED UPON. POLICE STATISTICS ARE THE REALISTIC BASE LINE FROM WHICH AN ACCOUNTING SHOULD BE GIVEN TO THE LARGE BODY OF DATA VALIDLY COMPILED AT LOCAL LEVELS. NEVERTHELESS, MORE CAREFULLY PUBLISHED AND DETAILED REPORTS BY LAW ENFORCEMENT AGENCIES ARE ALSO NEEDED, MANY POLICE OF THE MAJOR URBAN AREAS ARE SO UNCLEAR AND INCONSISTENTLY ASSEMBLED AT PRESENT THAT THEY ARE ALMOST WORTHLESS IN A SCIENTIFIC SENSE. CAREFUL EXPLANATIONS OF THE METHOD OF ASSEMBLY OF THE DATA AND THEIR FLUCTUATIONS SHOULD BE GIVEN AND UNITS OF COUNT SHOULD BE DEFINED ALONG WITH ALL TERMS USED. BY FOCUSING ATTENTION UPON THOSE WELL-DESIGNED LOCAL STATISTICAL POLICE SYSTEMS, AS THEY ARE INTRODUCED AND MAINTAINED, KNOWLEDGE OF THE CRIME PROBLEM IN ITS MANY VARIATIONS WILL BECOME MORE FIRMLY AND RELIABLY GROUNDED. TABLES SHOWING DATA FROM THE PHILADELPHIA POLICE STATISTICS ARE PROVIDED AS ARE FOOTNOTES. (AUTHOR ABSTRACT MODIFIED)