Classical test theory

Classical test theory (CTT) is a body of related <a href="/facts/Psychometric/56X26MDI">psychometric</a> theory that predicts outcomes of psychological <a href="/facts/Test_(assessment)/CjK7g99B">testing</a> such as the difficulty of items or the ability of test-takers. It is a theory of testing based on the idea that a person's observed or obtained score on a test is the sum of a true score (error-free score) and an error score. Generally speaking, the aim of classical test theory is to understand and improve the <a href="/facts/Reliability_(psychometric)/2QJrAeB5">reliability</a> of psychological tests.
Classical test theory may be regarded as roughly synonymous with true score theory. The term "classical" refers not only to the chronology of these models but also contrasts with the more recent psychometric theories, generally referred to collectively as <a href="/facts/Item_response_theory/4WmQgExu">item response theory</a>, which sometimes bear the appellation "modern" as in "modern latent trait theory".
Classical test theory as we know it today was codified by Novick (1966) and described in classic texts such as Lord & Novick (1968) and Allen & Yen (2002). The description of classical test theory below follows these seminal publications.

Classical test theory open-in-new

Classical test theory