Table II.
Commonly used test parameters in diagnostic studies
| Parameter | Formula | Definition |
|---|---|---|
| Sensitivity | TP / (TP + FN) | Proportion of positive result in infected patients |
| Specificity | TN / (TN + FP) | Proportion of negative result in noninfected patients |
| Positive predictive value (PPV) | TP / (TP + FP) | Proportion of infection among patients with a positive result |
| Negative predictive value (NPV) | TN / (TN + FN) | Proportion of no infection among patients with a negative result |
| Positive likelihood ratio (LR+) | Sensitivity / (1 - specificity) | Ratio of a positive result in infected patients to a positive result in noninfected patients |
| Negative likelihood ratio (LR-) | (1 - sensitivity) / specificity | Ratio of a negative result in infected patients to a negative result in noninfected patients |
| Accuracy | (TP +TN) / (TP + TN + FP + FN) | Global measure of performance |
| Youden’s index10 | Sensitivity + specificity - 1 | Global measure of performance |
TP, true positive; FP, false positive; FN, false negative; TN, true negative