Which statement describes specificity?

• A. The test correctly identifies most people who have the condition
• B. The test correctly excludes most people who do not have the condition
• C. The test has a high false positive rate
• D. Specificity is the proportion of true negatives among those who do not have the condition

Answer: (D)

Specificity is about correctly ruling out people who do not have the condition. It is defined as the proportion of true negatives among those who do not have the condition. This makes it a precise measure of how well a test avoids false positives. If a test has high specificity, most of the people without the condition will test negative.

The other ideas map to related concepts but not the exact definition: identifying most people who have the condition describes sensitivity, not specificity; a high false positive rate reflects low specificity; and saying the test correctly excludes most without the condition is a qualitative description, whereas the precise definition is the proportion of true negatives among those without the condition.