Question

CA-125 is a marker for the screening of ovarian cancer. To characterize this test, histopathological confirmation of ovarian cancer was done in a cohort of patients. 60 of 100 women who tested positive had ovarian cancer, and 20 of 100 women who tested negative had ovarian cancer. What is the negative predictive value of this test?

• A. 20/100
• B. 40/100
• C. 60/100
• D. 80/100

Hint:

NPV uses only the test-negative column: true negatives over all negatives.

Answer 1

The Correct Option is D

Step 1: Build the 2x2 table. Among 100 test-positive women, 60 have disease (true positives) and 40 do not (false positives). Among 100 test-negative women, 20 have disease (false negatives) and 80 do not (true negatives).
Step 2: Recall the formula. Negative predictive value is the chance that a person who tests negative truly does not have the disease: \[ NPV = \frac{TN}{TN + FN} \]
Step 3: Substitute. TN = 80 and FN = 20, so \[ NPV = \frac{80}{80 + 20} = \frac{80}{100} = 80\% \]
The negative predictive value is 80/100. Ref: Park's PSM, screening test validity.