Influence of Person Misfit on IRT Item Parameter Estimation and Data Purification
Xiaoyang Dai · Zhongguo linchuang xinlixue zazhi · 2011
Objective: Investigate the impact of person-misfit on item parameter estimation and the effect of data purification procedure.Methods: The two-parameter logistic model(2PL) and lz statistic were used in this study.ICC theory was used to evaluate the bias of item parameter estimation.And in this paper an approach to data purification was described and applied.Results: ①The more misfit a person,had the larger bias in model estimation;②The bias of item parameter estimation would reduce,when a test contained more items;③Sample size had limited influence on the ability of lz;④The power of lz statistic was increased by data purification.Conclusion: Item parameters estimated from data including aberrants are biased and the power of lz,as a consequence,is underestimated.It is shown that by a data purification procedure,the recovery of the power of the lz is achieved.