In a study of 200 subjects, a new point-of-care test for tuberculosis is compared with culture (gold standard). Among 50 culture-positive subjects, 40 test positive. Among 150 culture-negative subjects, 30 test positive. The specificity of the new test is:

• A 57.1%
• B 82.4%
• C 88.0%
• D 80.0% ✓

Explanation

Specificity = True Negatives / (True Negatives + False Positives). True Negatives = 150 − 30 = 120. False Positives = 30. Specificity = 120 / 150 = 80.0%. Sensitivity = 40/50 = 80%, and PPV = 40/70 = 57.1%; these are distractors. Specificity reflects ability to correctly identify non-diseased subjects.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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