Item Response Theory

An item refers to an individual question in a test or questionnaire. In educational and psychological testing, there are usually many items in a test. According to item response theory (IRT), a person’s performance on a specific test item is determined by the amount of some underlying trait that the person possesses. The underlying trait is a latent variable and sometimes referred to as ability or proficiency. IRT can be seen as modern test theory, and classical test theory traditionally provides a means of performing test analysis and item analysis. Frederic M. Lord is credited with defining and developing IRT. This entry first discusses IRT in the context of classical test theory and explains IRT models. The entry then discusses the practical use of IRT.