Which property indicates an index measures what it is intended to measure?

• A. Reliability
• B. Validity
• C. Quantifiability
• D. Sensitivity

Answer: (B)

Validity is the extent to which an index measures what it is intended to measure. It explains why the tool’s results truly reflect the specific concept or construct you’re trying to assess, such as actual oral health status or behavioral patterns, rather than something else. If the scores correspond to the real phenomenon and allow correct inferences about that construct, the index is valid. Reliability, by contrast, is about consistency—an index can give the same results across repeated measurements but still not be valid if those results don’t reflect the true construct. Quantifiability is simply the ability to assign numbers to observations, not proof that those numbers capture the intended concept. Sensitivity refers to the tool’s ability to detect true cases or changes, which is about detection, not overall validity of the measurement.