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