TRISS Probability Calculator

About this calculator

TRISS (Trauma and Injury Severity Score), developed by Boyd, Copes and Champion in 1987 from the Major Trauma Outcome Study, estimates a patient's probability of survival (Ps) by combining physiological and anatomical severity into a single logistic model: Ps = 1 / (1 + e^-b), where b is a weighted sum of the Revised Trauma Score (RTS, built from Glasgow Coma Scale, systolic blood pressure and respiratory rate), the Injury Severity Score (ISS, the sum of squares of the three worst Abbreviated Injury Scale regions), and an age index.

Separate coefficient sets exist for blunt versus penetrating trauma, since survival odds at a given severity differ by mechanism. Trauma centers use TRISS scores retrospectively — comparing a patient's predicted Ps against their actual outcome (the "Ws" statistic) — to benchmark care quality and flag unexpected deaths or unexpected survivals for case review, not as a real-time bedside triage tool.