A new rapid test for tuberculosis is evaluated against culture as the gold standard. Among 200 patients with confirmed pulmonary tuberculosis, the test is positive in 170. Among 800 patients proven free of tuberculosis, the test is negative in 760. Which measure equals 760 divided by 800?

• A Sensitivity
• B Accuracy
• C Negative predictive value
• D Specificity ✓

Explanation

Specificity is the proportion of truly non-diseased persons who test negative, that is true negatives divided by all non-diseased. Here 760 of 800 culture-negative patients test negative, giving 95%. Sensitivity would be 170 divided by 200 (85%). Predictive values depend on disease prevalence in the tested population, whereas sensitivity and specificity are intrinsic properties of the test compared with the gold standard.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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