Laboratory Testing
Calculating Predictive Value
The following table shows how to calculate positive and negative predictive values.
| Condition (as determined by the gold standard) | ||||
|---|---|---|---|---|
| Present | Absent | |||
| Test Outcome | Positive | True Positive a | False Positive b | Positive predictive value PPV = TP/(TP+FP) =a/(a+b) |
| Negative | False Negative c | True Negative d | Negative predictive value NPV = TN/(FN+TN) =d/(c+d) | |
| Sensitivity a/(a+c) |
Specificity d/(b+d) |
|||
Here is an example of how these formulas would be used:
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