A screening programme is extended from a low-prevalence district to a high-prevalence district using the same test with unchanged sensitivity and specificity. Compared with the low-prevalence district, the new setting will show:

• A Both predictive values remain unchanged
• B Lower positive predictive value and higher negative predictive value
• C Both predictive values increase
• D Higher positive predictive value and lower negative predictive value ✓

Explanation

Sensitivity and specificity are intrinsic properties of the test and do not change with prevalence. Predictive values depend heavily on prevalence: as prevalence rises, a positive result is more likely to be truly diseased, so PPV rises, while a negative result is less reassuring because more cases slip through, so NPV falls. Option C confuses predictive values with accuracy measures such as sensitivity.

Reference: Gordis Epidemiology, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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