**Which of the following is incorrect?**

A. Sens = TP/(TP+FN); Spec = TN/(TN+FP)

B. PPV = TP/(TP+FP); NPV = TN/(TN+FN)

C. Positive likelihood ratio (LR+) = sens/(1 - spec)

D. Post-test probability = pre-test probability x likelihood ratio

**Answer**: D

Post-test odds = pre-test odds x likelihood ratio, where odds = probability/(1-probability)

A clear knowledge of the above is essential to critically appraise articles on diagnostic methods, e.g. to compare a new diagnostic method to the gold standard.

**Reference**

Centre for Health Evidence