A Sampling Model for Validity

A multifacet sampling model, based on generalizability theory, is developed for the measurement of dispositional attributes. Dispositions are defined in terms of universes of observations, and the value of the disposition is given by the universe score, the mean over the universe defining the disposition. Observed scores provide estimates of universe scores, and errors of measurement are introduced in order to maintain consistency in these estimates. The sampling model provides a straightforward interpretation of validity in terms of the accuracy of estimates of the universe scores, and of reliability in terms of the consistency among these estimates. A third property of measurements, import, is defined in terms of all of the implications of a measurement. The model provides the basis for a detailed analysis of standardization and of the systematic errors that standardization creates; for example, the hypothesis that increases in reliability may cause decreases in validity is easily derived from the model. The model also suggests an explicit mechanism for relating the refinement of measurement procedures to the development of laws and theories.