Item response theory

As mental test theories, both CTT and IRT address similar issues of measurement. Compared to CTT, IRT serves asan alternative test theory that bears several desirable features. These features include the following: (a) direct incorporation of item indices (e.g., item difficulty, discrimination) in the measurement model, (b) provision of different standard errors for individual score levels, and (c) common scale measurement of persons and items. As a result, IRT is a theoretically more complete framework than CTT for solving a wide variety of measurement problems such as test equating, detection of differential item functioning (DIF), test construction, computerized adaptive testing, identification of poorly measured individuals, and so forth.