FIGURE 5.

Effect of number of covariates (k) in risk model on resubstitution bias in AUC. Population box plot represents true AUC distribution in interested population at large. Sample box plot represents distribution of AUC derived from sample dataset used to construct risk model. Each box plot was based on 1,000 simulations. When k = 5, there is slight upward (optimistic) bias in sample AUC distribution compared with true population. Degree of optimistic bias increases drastically when k increases to 50.