Psychology as an empirical science depends on the availability of valid measures of a construct. Validity means that a measure (e.g., a test or questionnaire) adequately assesses the construct (trait) it intends to measure. In their 1959 article “Convergent and Discriminant Validation by the Multitrait–Multimethod Matrix,” Donald T. Campbell and Donald W. Fiske proposed a way of test validation based on the idea that it is not sufficient to consider a single operationalization of a construct but that multiple measures are necessary. In order to validate a measure, scientists first have to define the construct to be measured in a literary form and then must generate at least two measures that are as different as possible but that are each adequate for [Page 255]measuring the ...