1. Faculty of Psychology, Southwest University, Chongqing 400715, China; 2. Southwest University Branch, Collaborative Innovation Center of Assessment toward Basic Education Quality, Chongqing 400715, China
Abstract：This research proposed the Polytomous Cognitive Diagnosis Testlet Model (PCDTM), which is suitable for polytomous response assessment with a multidimensional testlet effects structure. To investigate the performance of the PCDTM, we presented a simulation and an empirical study. Results indicated that: (1)The PCDTM model is reasonable and effective, and accurate parameter estimation results can be obtained regardless of whether the answer data contain testlet effects or not; (2) as the sample size, item quality, and the number of item increase, the accuracy of estimation of the examinees' parameters, item parameters, and testlet parameters would be improved; (3) ignoring testlet effects will decrease the item parameter estimation accuracy and the examinees' accuracy rate, and even the estimation results may be confused; (4) the results of the empirical study of the 2012 large-scale test in mathematics also show that the PCDTM model fits better and has accurate parameter estimation, which is more suitable for processing testlet data in actual data. We suggested that when using this model, the sample size should not be less than 1000, and the test length should not be less than 20 items.
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