Positive predictive value
Positive predictive value of a test/investigation is defined as the proportion of patients with positive results being truly diseased.
Positive predictive value = true positives (TP) detected / total positive results
(total positive results = true positive (TP) + false positive (FP)
One can also determine the PPV with an estimate of sensitivity, specificity, and pretest probability (p).
PPV = [(sensitivity) x (p)] / [sensitivity x (p) + (1 - specificity) x (1 - p)]
- unlike sensitivity and specificity, PPV is highly dependent on the prevalence of the disease in the target population