The logistic regression concordance rate is a measure of concordance between predicted and observed risk between all possible case-control pairs. Pairs are considered to be concordant if the predicted risk for the case is higher than the predicted risk for the control, and discordant if the opposite is true. We employed “leave-one-out” cross-validation as implemented in SAS Proc Logistic (SASInstituteInc 2002–03) to compute predicted risk scores and concordance rates. In this procedure, the risk for each observation was predicted from a model parameterized on all other observations. This approach reduces inflated concordance rates that result from over-fitting.
