What this calculator does
Youden's index works out combines a test’s sensitivity and specificity into one score of diagnostic performance. Enter your own figures above and the answer updates as you type: nothing is fixed in the code, so the result reflects exactly the numbers you supply.
The formula this calculator evaluates is printed under the tool and explained below, so you can check the working by hand or reuse it in a spreadsheet.
The formula
FormulaYouden's J = sensitivity + specificity − 1, ranging from 0 (no better than chance) to 1 (perfect test)
The inputs explained
| Field | What to enter |
|---|---|
| Sensitivity (%) (%) | A number, measured in %. Starts at 90. |
| Specificity (%) (%) | A number, measured in %. Starts at 85. |
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the answer changes with sensitivity (%)
Every other input is held at the calculator’s starting values while sensitivity (%) varies. Select any row to load that scenario into the calculator.