Estimating and Fitting the Non-continuous category scored Polytomous Items under the Weighted Score Logistic Model and its Simulation Study

Abstract

This study presents a novel extension of the weighted score logistic model (WSLM). The WSLM is an advancement of the traditional dichotomous logistic model that incorporates an additional weighted score parameter. This model is specifically designed to analyze non-continuous category scored polytomous items in educational and psychological testing contexts. Within the WSLM framework, the mean difficulty parameter reflects the overall item difficulty, while both discrimination and mean difficulty parameters are estimated using marginal maximum likelihood estimation. A Monte Carlo simulation study was conducted to evaluate the performance of the WSLM, which demonstrated low levels of bias and root mean square error (RMSE) of item parameters, indicative of accurate parameter recovery. Under most simulation conditions, the fit statistics Q1 and Q4 for polytomous items under the WSLM remained below their respective critical chi-square values, suggesting acceptable model-data fit. These results support the applicability and robustness of the WSLM in practical assessment settings involving complex scoring schemes.

Keywords

polytomous models weighted score logistic model polytomous items model fit item response theory

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