08/11/2006, 14:30 — 15:30 — Room P3.31, Mathematics Building Márcia D'Elia Branco, DE/IME, Universidade de São Paulo

A Skew-Normal Item Response Theory Family

Normal assumptions for the latent variable and symmetric item characteristics curves have been used in the last 50 years in many psychometric methods for item-response theory (IRT) models. However this assumption can be restrictive for modeling human behavior. This paper introduces a new family of asymmetric models for item response theory, namely the skew-normal item response theory (SN-IRT) model. This family extends the symmetric ogive normal model by considering: a) an accumulated skew-normal distribution for the item characteristic curve and b) a skew-normal distribution for the latent variables modeling the individuals? abilities. Hence, the SN-IRT is a more flexible model for fitting data sets with dichotomous responses. Bayesian inference methodology using two data augmentation approaches for implementing the MCMC methodology is developed. Model selection is considered by using several Bayesian criteria. An application is conducted and the proposed penalization parameter is interpreted in the context of a data set related to a mathematical test applied to Peruvian students in rural schools.