A new screening test for a rare infectious disease has a sensitivity of 95% and specificity of 90%. If the prevalence of the disease in the population decreases, what happens to the Negative Predictive Value (NPV) of the test?
- A NPV decreases
- B NPV increases ✓
- C NPV remains unchanged
- D NPV becomes equal to sensitivity
Correct answer: B. NPV increases
Explanation
Negative Predictive Value (NPV) is inversely related to disease prevalence. As prevalence decreases, the proportion of true negatives among all negative test results increases, thereby increasing the NPV. Conversely, Positive Predictive Value (PPV) decreases with lower prevalence because a higher proportion of positive results will be false positives. Understanding this relationship is vital for interpreting screening tests in low-prevalence settings.
Reference: Park's Textbook of Preventive and Social Medicine, 26th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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