The Effectiveness of Risk Scores: the Logit Rank Plot


J. Copas Department of Statistics, University of Warwick, Coventry, CV4 7AL, UK


A risk score s for event E is a function of covariates with the property that P(E|s) is an increasing function of s. Motivated by applications in medicine and in criminology, we suggest the logit rank plot as a good way of summarizing the effectiveness of such a score. Explicitly, plot logit{P(E|s)} against logit(r), where r is the proportional rank of s in a sample or population. The slope of this plot gives an overall measure of effectiveness, and the logit rank transformation provides a common basis on which different risk scores can be compared. Some practical and theoretical aspects are discussed.