Injury severity measurement is important for meaningful comparison of outcomes of trauma care, and assessment of burden of injury. Trends in hospital separations are often used as a proxy for trends in population incidence. These trends can be misleading due to variations over time or between places in factors unrelated to incidence, such as admission policies and practices. Injury severity measurement is a promising basis for improving measurement of trends in the population incidence of injury, as the incidence of serious injury is less likely to be affected by extraneous factors (Cryer & Jarvis 1999).

Different injury severity criteria are potentially of interest depending on the application. These include threat-to-life (probability of death), cost, impairment, incapacity, impact on quality of life, and disability (Langley & Cryer 2000; Cryer & Langley 2002).