What does specificity measure in a diagnostic test?

Specificity in a diagnostic test refers to the test's ability to correctly identify individuals who do not have the disease, thereby measuring the proportion of true negatives among all those who are truly negative. In other words, a test with high specificity effectively reduces the proportion of false positives, ensuring that people who do not have the condition are accurately identified as negative.

When evaluating a diagnostic test, it's important to differentiate specificity from sensitivity. Sensitivity measures how effectively a test identifies those with the disease (true positives). On the other hand, specificity focuses on correctly identifying those without the disease (true negatives). Therefore, specificity is particularly crucial when the consequences of false positives are significant, as it helps ensure that individuals are not incorrectly diagnosed with a condition they do not have.

The other concepts in the question do not accurately capture the essence of specificity. The overall accuracy of a test would incorporate both true positives and true negatives but does not focus solely on the identification of negative results. Similarly, precision refers more to reproducibility of results rather than the capacity to determine the absence of disease. Understanding this distinction is critical for effectively interpreting diagnostic tests.