Item response theory (IRT), also called latent trait theory, is a psychometric theory that was created to better understand how individuals respond to individual items on psychological and educational tests. The underlying theory is built around a series of mathematical formulae that have parameters that need to be estimated using complex statistical algorithms. These parameters relate to properties of individual items and characteristics of individual respondents. The term latent trait is used to describe IRT in that characteristics of individuals cannot be directly observed; they must be inferred by using certain assumptions about the response process that help estimate these parameters.

IRT complements and contrasts classical test theory (CTT), which is the predominant psychometric theory taught in undergraduate and graduate programs. CTT differs from IRT in ...

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