Figure 3

Receiver operating characteristic (ROC) curves for disease diagnosis based on the numbers of symptoms. Red dots = the set of sensitivities and specificities with the largest difference in the absolute values between 1 and the sums of sensitivities and specificities in a ROC curve. For each number of symptoms used for disease diagnosis, one red dot—a best set of sensitivities and specificities—was selected. With a maximum of 40 symptoms used for disease diagnosis, ROC curves in this figure were created assuming the risk ratio as 2, baseline symptom incidence as 0.1, proportions diseased as 0.05, no correlations between diseases, and no correlations between symptoms.