ABSTRACT
Mixture IRT models are based on the assumption that the population being measured is composed of two or more latent subpopulations, each of which responds to a set of tasks in predictably different ways. Within each subpopulation, a latent trait model holds for the entire set of tasks; however, between the subpopulations, there are differences that cannot be described within the constraints of the latent trait model used for a given subpopulation.
