Which statement correctly defines validity?

• A. The index yields consistent results across examiners.
• B. The index measures what it is intended to measure.
• C. The data can be recorded numerically.
• D. The index can detect small changes in health status.

Answer: (B)

Validity is the extent to which an instrument measures what it is intended to measure. This captures the accuracy of the tool in representing the specific construct you want to assess, making it the best description of what validity means. The other statements describe related properties that are not validity: measuring consistency across examiners refers to reliability, not validity; data being recordable numerically concerns data type or measurement scale; and detecting small changes in health status speaks to responsiveness or sensitivity to change, not to whether the instrument measures the right concept. For a practical example, a periodontal health index should align with actual gum health findings to be valid, meaning it truly reflects the intended condition.