Chapter 7: Item Response Theory

David Thissen & Lynne Steinberg

Item response theory Item response theory (IRT) is a collection of mathematical models and statistical methods used for two primary purposes: item analysis and test scoring. Subsidiary uses of IRT include the design and assembly of tests and questionnaires, and the investigation of the structure of cognitive and affective constructs. IRT is used with data arising from educational tests of ability, proficiency or achievement as well as psychological questionnaires measuring attitudes or personality traits or states. As a tool for item analysis, IRT makes explicit the fact that many tests and questionnaires are intended to measure individual differences on some unobserved, or latent , construct. 1 By introducing an explicit model for the relations of the item responses to that latent variable, IRT can be used to obtain parameter estimates that are more straightforwardly interpretable in item analysis and test construction than the more indirect statistical summaries used in IRT ...

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