Validity

Validity is a core concept in logic and evidence. In formal logic, a deductive argument is valid if the conclusion follows necessarily from the premises based on its form; the truth of the premises is irrelevant to validity. A valid argument can have false premises; what matters is that, if the premises were true, the conclusion would be true.

Validity in measurement concerns whether a tool measures the intended concept. Types include content validity (domain coverage), construct validity (the extent to which scores relate to the theoretical construct, including convergent and discriminant validity), and criterion validity (correlation with external criteria; predictive and concurrent). Face validity assesses apparent relevance. External validity (generalizability) and ecological validity describe how well results generalize to real-world settings.

In research design, internal validity concerns whether observed effects are caused by the experimental manipulation rather than confounds; external validity concerns generalization to other populations or settings. Statistical conclusion validity concerns whether statistical inferences are appropriate given the data.

In law, validity refers to legality or enforceability: a contract or statute is valid if it meets applicable rules and can be enforced within the jurisdiction.

Validity is contextual and multifaceted; assessment requires clear definitions, appropriate methods, and awareness of limitations. Across disciplines, improving validity involves aligning methods with intended constructs or arguments, controlling for sources of bias, and carefully evaluating whether conclusions follow from the available evidence.