Validity is defined as the ability of a test to accurately indicate which individuals have a disease and which do not. Which statement best captures validity?

• A. It measures the test’s consistency across time.
• B. It measures the accuracy of the test in correctly classifying individuals.
• C. It measures the test’s practicality in the field.
• D. It measures the test’s cost-effectiveness.

Answer: (B)

Validity asks whether a test truly measures what it’s supposed to measure in terms identifying who has the disease and who does not. In practice, this means the test’s classifications should reflect reality—few misclassifications of diseased and non-diseased people. A valid diagnostic test will show high accuracy in distinguishing between those with and without the disease, which is closely connected to its sensitivity (how well it detects true positives) and specificity (how well it excludes true negatives).

The other aspects—being consistent across time, practical usefulness in the field, and cost-effectiveness—relate to reliability, feasibility, and economic considerations, not validity. A test can be consistent but still not valid if it repeatedly misclassifies people. It can be easy to use or inexpensive but fail to correctly identify disease status.