Item response theory modeling in health outcomes measurement.

There is a great need in health outcomes research to develop instruments that accurately measure a person's health status with minimal response burden. This need for psychometrically sound and clinically meaningful measures calls for better analytical tools beyond the methods available from traditional measurement theory. Applications of item response theory (IRT) modeling have increased considerably because of its utility for instrument development and evaluation, scale scoring, assessment of cultural equivalence, instrument linking and computerized adaptive testing. IRT models the relationship between a person's response to a survey question and their standing on a health construct, such as fatigue or depression. This review will discuss the theory and basics of IRT models and applications of these models to health outcomes measurement.