Notes on the Overlap Measure as an Alternative to the Youden Index: How Are They Related?

The ROC (Receiver Operating Characteristic) curve is frequently used for evaluating and comparing diagnostic tests. The Youden index, as one of the ROC summary index, measures the effectiveness of a diagnostic marker and enables the selection of an optimal threshold value (cut -off point) for the marker. Recently, the overlap coefficients (OVL), which capture the similarity between two distributions directly, are considered as alternative indices for determining the diagnostic performance of markers, that is, larger (smaller) overlap indicating poorer (better) diagnostic accuracy. This paper compare s the similarities and dissimilarities of the Youden index and OVL measures as well as the advantages of OVL measures over the Youden index in some situations. Numerical examples as well as a real data analysis with differentially expressed gene biomarkers are provided.