What is reliability?

• A. The consistency with which an instrument or rater measures a variable
• B. The extent to which a measure represents all facets of a given concept
• C. The accuracy of measurement relative to a gold standard
• D. The ability to predict outcomes

Answer: (A)

Reliability means the consistency of a measurement across time, raters, or items. It asks whether repeated measurements under similar conditions yield similar results, indicating low random error. For example, a goniometer that gives the same knee angle when measured by the same clinician on different occasions demonstrates good reliability, and two clinicians getting similar scores shows good inter-rater reliability. It’s possible for a tool to be reliable yet not valid, meaning it’s precise but not measuring what it’s supposed to measure. The description that defines reliability best is about consistency of measurement; the other options describe aspects of validity rather than reliability.