IRT Models - DRAFT VERSION

Item response theory is comprised of a set of statistical models that describe the relationship between assessment items and proficiency in some subject or skill area. In these models, proficiency is taken as a latent trait, indirectly observed through examinees performance on test items. IRT models assume that an examinee’s performance on each item reflects characteristics of the item and characteristics of the examinee. While an infinite variety of models is possible, those in most common use, such as the one, two, and three-parameter logistic models, characterize items by the level of proficiency that they require and precision with which item performance reflects proficiency along that trait. Examinees are characterized by their proficiency. Examinee’s performance on a particular item reflects item difficulty, his or her proficiency, and the effects of other forces that are not correlated across items or individuals.