FIRST, THE STATISTICAL ANALYSIS OF INJURY SEVERITY IS INTRODUCED BY CONSIDERING THE FOLLOWING TOPICS: (I) INTERPRETATION OF THE RECORDED GRADES OF INJURY SEVERITY (E.G. FATAL, SERIOUS, SLIGHT, NONE) AS DIVISIONS OF A CONTINUOUS SCALE. (II) THE POSSIBLE PRESENCE OF ERRORS IN RECORDING INJURY SEVERITY. (III) HOW THIS IS USED IN THE STATISTICAL ANALYSIS OF INJURY SEVERITY DATA, INCLUDING DISCUSSION OF COMPUTING METHODS. SECONDLY, ATTENTION IS TURNED TO DATA IN WHICH THE SEVERITIES OF INJURY TO TWO PEOPLE IN THE SAME CRASH IS GIVEN. BRITISH ACCIDENT DATA FOR 1969-72 HAS BEEN PROCESSED TO GIVE A CROSS-TABULATION OF THE SEVERITY OF INJURY TO THE DRIVER AND TO THE FRONT SEAT PASSENGER IN FOUR TYPES OF SINGLE-VEHICLE ACCIDENTS (OVERTURNING AND NONOVERTURNING, EACH IN RURAL AND IN URBAN AREAS). THREE COMPLICATIONS WITH THIS DATA ARE THAT THE NUMBER OF NON-INJURY ACCIDENTS IS UNKNOWN, THAT THE CASES WHERE A PASSENGER WAS PRESENT BUT UNINJURED COULD NOT BE DISTINGUISHED FROM THOSE WHERE THERE WAS NO PASSENGER, AND THAT THERE IS INCONSISTENCY IN THE POSITIONING OF THE THRESHOLDS SEPARATING SERIOUS FROM SLIGHT INJURY, AND SLIGHT FROM NO INJURY. A POSITIVE CORRELATION BETWEEN THE SEVERITIES OF INJURY TO THE TWO OCCUPANTS IS EVIDENT IN THE DATA. THIS IS INTERPRETED AS BEING LARGELY DUE TO THE SPEED OF THE CRASH, AND A MODEL IS DEVELOPED IN WHICH THE TWO SEVERITIES JOINTLY HAVE A BIVARIATE NORMAL DISTRIBUTION.(Author/publisher).
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