The receiver operationg characteristic (ROC) curve is a two-dimensional measure of classification performance depicting the trade-off between sensitivity and specificity. It is used in the analysis of a diagnostic test or screening test that classifies experimental units into two categories such as diseased (D)ornondiseased (D). Screening and laboratory test results are usually reported as a continuous variable. For example, the risk variable serum concentration of creatine phosphokinase for myocardial infarction (D) is approximately normally distributed varying from less than 100 units/ml to greater than 4,000 units/ml. The serum concentration of creatine phosphokinase for those without myocardial infarction (D) also has an approximate normal distribution but has a different mean (see Figure 1). Suppose that we dichotomize the serum concentration by some cutpoint so that values ...