Define sensitivity and specificity in the context of a health screening test.

• A. Specificity is the ability to correctly identify those without the disease (true negatives); Sensitivity is the ability to correctly identify those with the disease (true positives)
• B. Sensitivity is the ability to correctly identify those with the disease (true positives); Specificity is the ability to correctly identify those without the disease (true negatives)
• C. Sensitivity is the speed of the test; Specificity is the cost of the test
• D. Sensitivity and specificity are interchangeable

Answer: (B)

Understanding how a screening test performs hinges on two measures: sensitivity and specificity. Sensitivity is the test’s ability to correctly identify those who have the disease (true positives). Specificity is the test’s ability to correctly identify those without the disease (true negatives). This means a highly sensitive test catches most people who actually have the condition, so a negative result makes the disease unlikely (useful for ruling out). A highly specific test correctly labels most disease-free individuals as negative, so a positive result strongly suggests disease (useful for confirming). The statement that defines sensitivity as identifying those with the disease and specificity as identifying those without the disease is the accurate pairing. Speed or cost aren’t definitions of these metrics, and the terms aren’t interchangeable because they measure different aspects of accuracy. For example, with 20 diseased people out of 100 and a test that’s 90% sensitive and 95% specific, you’d get 18 true positives, 2 false negatives, 76 true negatives, and 4 false positives.