Validity

In psychology and assessment, validity is the extent to which a test measures what it claims to measure. A valid depression scale produces scores that actually reflect depression rather than general distress, mood, or response style.

Validity isn't a single property but a body of evidence — typically built up over many studies — that supports interpretations of test scores. Several types are commonly distinguished, including content validity (does the test cover the construct?), criterion validity (does it correlate with relevant external measures?), and construct validity (does it behave the way theory predicts?).