A study tests a new cardiac biomarker. The Receiver Operating Characteristic (ROC) curve for this marker gives an Area Under the Curve (AUC) of 0.72. Which statement best describes this result?

• A The test correctly classifies 72% of subjects regardless of cut-off
• B The test has a 72% sensitivity and 72% specificity at all thresholds
• C The test has 28% better discriminatory ability than chance alone
• D A random diseased subject will have a higher test result than a random non-diseased subject 72% of the time ✓

Explanation

AUC represents the probability that a randomly selected diseased individual will have a higher (more abnormal) test result than a randomly selected non-diseased individual — this is the concordance statistic. AUC 0.5 equals chance; AUC 1.0 is perfect. Option A conflates AUC with overall accuracy; option B is incorrect because sensitivity and specificity change with every cut-off value.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

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