INFORMATION THEORY AND SIGNAL DETECTION THEORY TECHNIQUES WERE USED TO ASSESS THE VALIDITY OF POLICE REPORTED TRAFFIC ACCIDENT DATA. THE VALIDITY CRITERIA WERE THE DATA AND CONCLUSIONS OF MULTI-DISCIPLINARY ACCIDENT INVESTIGATION TEAMS WHO INVESTIGATED THE SAME TRAFFIC ACCIDENTS. THE RESULTS INDICATED THAT THE ACCIDENT LEVEL VARIABLES REPORTED BY THE POLICE WITH LEAST RELIABILITY WERE VERTICAL ROAD CHARACTER, ACCIDENT SEVERITY, AND ROAD SURFACE COMPOSITION. THE MOST RELIABLY REPORTED DATA WERE THOSE CONCERNED WITH THE ACCIDENT LOCATION, DATE, AND NUMBER OF DRIVERS, PASSENGERS, AND VEHICLES. THE INFORMATIVENESS OF THE POLICE REPORTS WITH RESPECT TO DRIVER/VEHICLE CHARACTERISTICS WAS PRACTICALLY NIL, WITH THE EXCEPTION OF DRIVER AGE, SEX AND VEHICLE MODEL FOR WHICH THE POLICE WERE CORRECT MOST OF THE TIME (BUT NOT ERRORLESS). IT WAS ALSO FOUND THAT POLICE REPORTS PROVIDED VERY LITTLE INFORMATION REGARDING THE PRESENCE OF DIFFERENT HUMAN CONDITIONS AND STATES, VEHICLE DEFECTS AND ENVIRONMENTAL/ROAD DEFICIENCIES. THE SENSITIVITY OF POLICE INVESTIGATORS TO ALL ACCIDENT CAUSES WAS LOW. WHEN CAUSES WERE CATEGORIZED INTO HUMAN DIRECT, HUMAN INDIRECT (CONDITIONS AND STATES) VEHICLE, AND ENVIRONMENTAL, POLICE WERE THE MOST RELIABLE WITH RESPECT TO HUMAN DIRECT CAUSES AND THE LEAST RELIABLE WITH RESPECT TO ENVIRONMENTAL AND HUMAN INDIRECT CAUSES. IMPLICATIONS FOR IMPROVEMENT AND USE OF POLICE DATA ARE DISCUSSED. (Author/publisher).
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