Indexes of severity: underlying concepts--a reply.

A recent paper on the concepts underlying six indexes of severity that have been proposed for health services research claimed to identify deficiencies in each. A close examination reveals that the criticisms are generally without substance, and that the claim that the indexes "violate some of the principles implied by their formulation" is in error. Most of the objections apparently stem from fundamental confusion concerning the use of such indexes. Two of the indexes in question, the Abbreviated Injury Scale AIS) and the Injury Severity Score (ISS), have been validated and are being used widely both in the United States and elsewhere as the principal descriptors of trauma in motor vehicle crashes. The use of these indexes has contributed significantly to motor vehicle crash research and to the improvements in vehicles and highways that are reducing the trauma resulting from such crashes.