What is the Youden Index?
The Youden Index (also called the J statistic) is a single summary measure of a diagnostic or classification test’s overall accuracy, combining both sensitivity and specificity into one number.
The formula
J = Sensitivity + Specificity − 1. J ranges from −1 to 1 (using proportions), with 0 indicating a test performs no better than chance and 1 indicating a perfect test with no false positives or false negatives.
The Youden Index is often used to help choose an optimal cutoff point on a ROC curve. This calculator is for general educational and statistical planning purposes.
Last reviewed August 2026