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Chapter 46: Item Response Theory
Item response theory (IRT) is commonly used in the construction of psychological scales and educational assessments (e.g. Hambleton et al., 1991). It provides an alternative to classical test theory (CTT), which was the predominant psychometric approach until the 1970s. IRT offers model-based measurement with convenient item banking (collections of calibrated items for use in new tests), evaluation of item bias (differential item function), test equating, computerized-adaptive testing, as well as standard errors for respondents at different points of the trait scale, rather than the equal errors of measurement assumed by CTT.
Models based on IRT involve a mapping of the 0 to 1 probability of an item being passed in a test, or endorsed in a questionnaire, to a ...