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This study explored the relationship between successful guessing and latent ability in dichotomous IRT models. Two new IRT models, the Rasch-Guessing model and the 2PL-Guessing model were developed with guessing functions integrating probability of guessing an item correctly with the examinee s ability and the item parameters. The conventional 3PL IRT model was compared with the new 2PL-Guessing model on parameter estimation using the Monte Carlo method. SAS program was used to implement the data simulation and the maximum likelihood estimation.

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Song Gao is working as an Institutional Research Analyst in Dixie State University of Utah. He received his B.A. degree in chemical engineering from Dalian University of Science & Technology. He earned both his M.S. degree in Workforce Education & Development and PH D degree in Educational Psychology in Southern Illinois University Carbondale.

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