Polytomous Item Response Theory Models provides a unified, comprehensive introduction to the range of polytomous models available within item response theory (IRT). It begins by outlining the primary structural distinction between the two major types of polytomous IRT models. This focuses on the two types of response probability that are unique to polytomous models and their associated response functions, which are modeled differently by the different types of IRT model. It describes, both conceptually and mathematically, the major specific polytomous models, including the Nominal Response Model, the Partial Credit Model, the Rating Scale model, and the Graded Response Model.

Nominal Response Model

Nominal Response Model

The nominal response model (NRM) was introduced by Bock (1972) as a way to model responses to items with two or more nominal categories. A standard example of such an item is a multiple-choice item where the distractors are chosen with no particular order in mind in terms of the trait ...

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