Severity indices and their implications for emergency medical services research and evaluation.

The present paper explores the rationale for the development of severity indices and the role such indices can play in various research and evaluation situations. Concrete examples from Emergency Medical Services research and evaluation settings are used to illustrate the potential shortcomings of designs that fail to incorporate measures of severity. A short critical review of existing indices is presented, and the ways that the indices can be refined and improved, and better used to evaluate emergency care, are summarized.