In a study evaluating a new rapid antigen test for typhoid, the receiver operating characteristic (ROC) curve is plotted. The area under the ROC curve (AUROC) is 0.91. Which of the following is the MOST accurate interpretation of this finding?
- A The test correctly classifies 91% of all individuals regardless of disease status
- B The sensitivity of the test at all cut-offs averages 91%
- C There is a 91% probability that a randomly selected diseased person has a higher test score than a randomly selected non-diseased person ✓
- D The test has a specificity of 91% at the optimal cut-off
Correct answer: C. There is a 91% probability that a randomly selected diseased person has a higher test score than a randomly selected non-diseased person
Explanation
The AUROC represents the probability that a randomly chosen case will have a higher test value than a randomly chosen non-case; an AUROC of 0.91 indicates excellent discrimination. It is not the same as overall accuracy, nor is it an average sensitivity or a specificity at any single cut-off. An AUROC of 0.5 indicates no discrimination (equivalent to chance), while 1.0 indicates perfect discrimination.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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