Youden Index Calculator
Enter sensitivity, specificity, and disease prevalence to compute the Youden J index and predictive values.
Youden index (J): 0.7700
Youden index (%): 77.00%
Positive predictive value (PPV): 67.15%
Negative predictive value (NPV): 96.96%
How to Use This Calculator
- Enter test sensitivity and specificity (between 0 and 1).
- Provide disease prevalence to contextualize predictive values.
- Review the Youden index and predictive values to assess diagnostic performance.
- Use the index to compare potential cutoffs or diagnostic tests.
Formula
Youden index J = Sensitivity + Specificity − 1
PPV = [Sensitivity × Prevalence] / [Sensitivity × Prevalence + (1 − Specificity) × (1 − Prevalence)]
NPV = [Specificity × (1 − Prevalence)] / [Specificity × (1 − Prevalence) + (1 − Sensitivity) × Prevalence]
Full Description
The Youden index summarizes diagnostic test accuracy by balancing sensitivity and specificity. Values range from −1 to 1, with 0 indicating no better than chance. Higher values indicate better discrimination between diseased and non-diseased individuals.
Predictive values supplement the Youden index by incorporating disease prevalence, reflecting real-world diagnostic utility.
Frequently Asked Questions
What does a Youden index of 0 mean?
The test has no discriminative ability; sensitivity equals 1 − specificity.
Can the Youden index be negative?
Yes. Negative values indicate the test performs worse than random chance.
Why include prevalence?
Prevalence affects PPV and NPV, informing real-world interpretation beyond sensitivity and specificity.
How to use Youden index in ROC analysis?
The cutoff maximizing Youden index on the ROC curve optimizes combined sensitivity and specificity.