validities

Validity refers to the degree to which evidence and theory support the interpretations of test scores or measurements for their intended use. A measure can be reliable without being valid, but it cannot be valid if it is not reliable. Validity is thus a property of the interpretations and uses, not of the instrument alone.

There are several families of validity. Content validity concerns whether a measure covers the full domain it intends to assess. Construct validity asks whether the measure behaves as theory predicts, including convergent validity (correlation with related constructs) and divergent validity (low correlation with unrelated ones), often examined via factor analysis.

Criterion validity includes predictive validity (how well scores predict future outcomes) and concurrent validity (correlation with an established criterion measured at the same time). Internal validity refers to causal inferences within a study, requiring control of confounding variables. External validity concerns generalizability to other settings, populations, and times, with ecological validity sometimes treated as a subset focusing on real-world contexts.

Face validity is a superficial judgment about whether a measure appears to assess the intended construct. In practice, researchers gather accumulating evidence across studies to support validity for a given use; no single study proves validity. Validity is a context-dependent property: a measure may be valid for one purpose but not for another.