An evaluation of road crash injury severity measures

Reliable and consistent measures of injury severity are necessary for the study of environmental, crash and personal factors involved in road traffic crashes. This study was designed to evaluate measures of injury severity derived from computerized hospital discharge records, using 3609 road crash casualties admitted to hospital in Western Australia in 1988. External cause of injury codes were used to identify injuries from road traffic crashes. The ICDMAP software was used to convert the diagnosis codes into Abbreviated Injury Scale (AIS) scores for each body region. The maximum AIS values were derived using (1) all 12 diagnosis codes; (2) the first six diagnosis codes; and (3) the principal diagnosis code alone. Other measures of injury severity evaluated were the number of body regions with at least one injury; the number of regions with Abbreviated Injury Severity score of three or more; and total number of days spent in hospital. Discriminant analysis suggested that the AIS could be separated into minor and major injuries at a score of three and the Injury Severity Score at a score of nine. The measures derived from the AIS were all strongly correlated with each other and with the length of hospital stay and the dichotomized values gave similar results to the other scores when used in regression analyses of the injury experience of different types of road users. It was concluded that measures incorporating elements of both severity and number of injuries were preferable but length of hospital stay would be a suitable proxy if no other injury information was available.