Youden Index Calculator Diagnostic Test

What the Youden Index Measures

The Youden index ($J$) summarizes diagnostic test accuracy in one number by combining sensitivity and specificity. It ranges from 0 to 1, with higher values indicating better overall performance. Related tools: Sensitivity and Specificity Calculator and Post-Test Probability Calculator.

Youden Index Formula

$$J = \text{sensitivity} + \text{specificity} - 1$$

Sensitivity is true positive rate. Specificity is true negative rate. A value of 0 means the test is no better than chance for the chosen threshold.

Example

With TP = 20, FN = 15, FP = 5, and TN = 40, sensitivity is $20/35 \approx 0.5714$, specificity is $40/45 \approx 0.8889$, and $J \approx 0.4603$.

Frequently Asked Questions

What is a good Youden index?

Values closer to 1 are better. In practice, $J > 0.4$ suggests useful accuracy, but acceptable cutoffs depend on the clinical or analytical context.

How is Youden index different from accuracy?

Accuracy mixes positives and negatives into one rate. Youden index focuses on how well the test identifies both diseased and non-diseased cases without ignoring class imbalance as strongly.

Can I enter sensitivity and specificity directly?

Yes. Switch input mode to enter percentages directly instead of confusion-matrix counts.

Why must each outcome group have cases?

Sensitivity needs at least one actual positive and specificity needs at least one actual negative. Otherwise the corresponding rate is undefined.

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Youden Index Calculator

What the Youden Index Measures

Youden Index Formula

Example

Frequently Asked Questions

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