Two Is Better Than One

Abstract

Psychologists too often rely on only one source of evidence to affirm the validity of a construct. However, they usually do not know all the conditions that can produce the evidence they gather. Hence, the inference is often limited to the data gathered and does not generalize to other categories of information. Examples of this habit are presented along with the suggestion that all social scientists should affirm the utility of their concepts with more than one class of information.