The new rules of measurement.

Abstract

Classical test theory, which the authors maintain applied psychologists are still too often exclusively taught, are contrasted with the new rules of measurement. In the newer, model-based version of test theory, called item response theory (IRT), some well-known rules of measurement o longer apply. Six old rules of measurement that conflict with the new rules are reviewed, and intuitive xplanations of the new rules are provided. Readers are also directed to additional informational sources about IRT, which, it is argued, every psychologist hould be familiar with. In an ever-changing world, psychological testing remains the flagship of applied psychology. Although both the context of application and the legal guidelines for using tests have changed, psychological tests themselves have been relatively stable. Many historically valued tests, in somewhat revised forms, remain in active current use. Further, although several new tests have de-veloped in response to contemporary needs in applied psychol-ogy, the principles underlying test development have remained constant. Or have they?