Evidence-appraisal glossary
Youden index
A single summary of a test's performance at a chosen cutoff, calculated as sensitivity plus specificity minus one, ranging from 0 for a useless test to 1 for a perfect one.
Also called: Youden's J, Youden's index.
The Youden index, written J, is often used to pick an optimal threshold for a continuous test by finding the cutoff that maximizes it, which corresponds to the point on the ROC curve farthest from the chance diagonal. Its appeal is simplicity, but maximizing J treats a false positive and a false negative as equally costly, which is rarely true in practice. When the consequences of the two errors differ, the threshold that maximizes J may not be the clinically best one.
Read the full Reading the Evidence blog.
This is a plain-language methodology definition for reading research. It is general education, not medical advice.