Youden Index Calculator
Evaluate diagnostic test performance with the Youden J statistic
Input Method
Confusion Matrix Values
Confusion Matrix
Correctly identified positive cases
Incorrectly identified as positive
Incorrectly identified as negative
Correctly identified negative cases
Youden Index Results
Interpretation
Fair test performance. The test shows moderate diagnostic value but may benefit from optimization or combination with other tests.
Current Value: 0.4603 indicates fair diagnostic performance
Example: COVID-19 Test
Confusion Matrix
True Positive: 85 (correctly identified infected)
False Positive: 10 (false alarms)
False Negative: 15 (missed cases)
True Negative: 90 (correctly identified healthy)
Calculations
Sensitivity: 85/(85+15) = 0.85
Specificity: 90/(90+10) = 0.90
Youden Index: 0.85 + 0.90 - 1 = 0.75
Result
Performance Interpretation
J ≥ 0.8: Excellent
Outstanding test with high accuracy
J ≥ 0.6: Good
Strong diagnostic performance
J ≥ 0.4: Fair
Moderate diagnostic value
J ≤ 0: No Value
No better than random chance
Key Applications
Medical Diagnostics: Evaluating clinical tests and screening procedures
Biomarker Research: Assessing diagnostic biomarker performance
Cut-off Optimization: Finding optimal threshold values
Test Comparison: Comparing multiple diagnostic methods
Understanding the Youden Index
What is the Youden Index?
The Youden Index (J statistic) is a single statistic that captures the performance of a dichotomous diagnostic test. It represents the test's ability to avoid failure, combining both sensitivity and specificity into one measure.
Key Advantages
- •Single Metric: Combines sensitivity and specificity
- •Threshold Independent: Useful for cut-off optimization
- •Easy Interpretation: Range from 0 to 1
Formula & Calculation
Youden Index Formula
J = Sensitivity + Specificity - 1
Also expressed as: J = TPR + TNR - 1
Component Formulas
Sensitivity = TP / (TP + FN)
Specificity = TN / (TN + FP)
Alternative Expression
J = TPR - FPR
True Positive Rate minus False Positive Rate
Step-by-Step Calculation
- 1.Obtain or calculate sensitivity (true positive rate)
- 2.Obtain or calculate specificity (true negative rate)
- 3.Apply the Youden formula: J = Sensitivity + Specificity - 1
- 4.Interpret the result using performance categories
Clinical Applications
- •Screening Tests: Cancer screening, disease detection
- •Biomarker Validation: Evaluating diagnostic markers
- •Test Optimization: Finding optimal cut-off points
- •ROC Analysis: Identifying best performance point