DIF Assessment for Polytomously Scored Items: A Framework for Classification and Evaluation

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Abstract
Increased use of alternatives to the traditional dichotomously scored multiple-choice item yield complex responses that require complex scoring rules. Some of these new item types can be polytomously scored. DIF methodology is well-defined for traditional dichotomously scored multiple-choice items. This paper provides a classification scheme of DIF procedures for dichotomously scored items that is applicable to new DIF procedures for polytomously scored items. In the process, a formal development of a polytomous version of a dichotomous DIF technique is presented. Several polytomous DIF techniques are evaluated in terms of statistical and practical criteria. Index terms: DIF methodology, differential item functioning, item bias, polytomous scoring, statistical criteria for differential item functioning