knowngroups

Knowngroups, usually written as known-groups or known groups in literature, refers to a method for evaluating the construct validity of a measurement instrument by testing whether the instrument can differentiate between groups that are known to differ on the target construct.

In practice, researchers identify groups that should differ a priori on the trait being measured—such as patients with a diagnosed condition versus healthy controls, or students at different educational levels. Data are collected and statistical analyses (t-tests, ANOVA, or nonparametric tests) compare mean scores or distributions. A meaningful difference, along with a substantial effect size, supports known-groups validity. Sometimes, receiver operating characteristic (ROC) analysis is used to assess discrimination performance.

Applications include patient-reported outcome measures, clinical scales, and educational assessments, where demonstrating the instrument’s ability to separate known groups helps substantiate that it measures the intended construct rather than incidental characteristics.

Limitations include the need for credible a priori group definitions, potential biases in group selection, and the possibility that observed differences reflect confounding variables rather than the construct itself. Known-groups validity is one facet of construct validity and complements other evidence such as convergent validity, discriminant validity, and criterion validity.