Advanced Research Methods for the Social and Behavioral Sciences

Item response theory (IRT) represents an alternative measurement approach to Classical test theory (CTT) that has been developed to address some of the key limitations in CTT. IRT utilizes a logistic function to jointly scale both person characteristics (e.g. ability) and task characteristics (e.g. difficulty) along a common metric, and is grounded upon the notion that different item sets should not result in different scaling solutions. This provides IRT with a number of advantages over CTT; namely that the performances of individuals who are administered different sets of tasks may still be justifiably compared. From this basis, the IRT approach has established its utility through its applications in such varied contexts as adaptive testing, cognitive diagnostic modeling, item difficulty modeling, and latent class analyses. The current chapter focuses on applied issues in measurement with IRT, with emphasis on its distinct advantages over traditional approaches.