On Some Statistical and Axiomatic Properties of the Injury Severity Score

The Injury Severity Score (ISS) is a standard aggregate indicator of the overall severity of multiple injuries to the human body. This score is calculated by summing the squares of the three highest values of the Abbreviated Injury Scale (AIS) grades across six body regions of a trauma victim. Despite its widespread usage over the past four decades, little is known in the (mostly medical) literature on the subject about the axiomatic and statistical properties of this quadratic aggregation score. To bridge this gap, the present paper studies the ISS from the perspective of recent advances in decision science. We demonstrate some statistical and axiomatic properties of the ISS as a multicrtieria aggregation procedure. Our study highlights some unintended, undesirable properties that stem from arbitrary choices in its design and that call lead to bias in its use as a patient triage criterion.