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Abstract

Discrimination has traditionally been parameterized for items but not other empirical factors. Consequently, if person factors affect discrimination they cause misfit. However, by explicitly formulating the relationship between discrimination and the unit of a metric, it is possible to parameterize discrimination for person groups. This article applies the Rasch model with a person group discrimination parameter to demonstrate the empirical effect of a person group factor on the degree of discrimination. The model is applied to the responses of students in different grades of schooling to a reading test, resulting in improved equating and fit of the data to the model. A simulation study confirms the efficacy of the model and tests of fit. Applied implications are discussed.

Keywords

Rasch model two-parameter logistic model 2PL sufficient statistic discrimination unit metric person group

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Modeling the Effects of Person Group Factors on Discrimination

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