A Mixture Rasch Model with a Covariate: a Simulation Study via Bayesian Markov Chain Monte Carlo Estimation

Title of Document: A MIXTURE RASCH MODEL WITH A COVARIATE: A SIMULATION STUDY VIA BAYESIAN MARKOV CHAIN MONTE CARLO ESTIMATION Yunyun Dai, Doctor of Philosophy, 2009 Directed By: Professor, Robert J. Mislevy, Department of Measurement, Statistics and Evaluation Mixtures of item response theory models have been proposed as a technique to explore response patterns in test data related to cognitive strategies, instructional sensitivity, and differential item functioning (DIF). Estimation proves challenging due to difficulties in identification and questions of effect size needed to recover underlying structures. In particular, the impact of auxiliary variables, or covariates, for examinees in estimation has not been systematically explored. The goal of this dissertation is to carry out a systematically designed simulation study to investigate the performance of mixture Rasch model (MRM) under Bayesian estimation using Markov Chain Monte Carlo (MCMC) method. The dependent variables in this study are (1) the proportion of cases in which the generating mixture structure is recovered, and (2) among those cases in which the structure is recovered, the bias and root mean squared error of parameter estimates. The foci of the study are to use a flexible logistic regression model to parameterize the relation between latent class membership and the examinee covariate, to study MCMC estimation behavior in light of effect size, and to provide insights and suggestions on model application and model estimation. A MIXTURE RASCH MODEL WITH A COVARIATE: A SIMULATION STUDY VIA BAYESIAN MCMC ESTIMATION