Polytomous Item Response Theory Models

Polytomous Item Response Theory Models provides a unified, comprehensive introduction to the range of polytomous models available within item response theory (IRT).AyIt begins by outlining the primary structural distinction between the two major types of polytomous IRT models.AyThis 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.AyIt 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.AyImportant variations, such as the Generalized Partial Credit Model are also described as are less common variations, such as the Rating Scale version of the Graded Response Model. Relationships among the models are also investigated and the operation of measurement information is described for each major model.AyPractical examples of major models using real data are provided, as is a chapter on choosing an appropriate model.AyFigures are used throughout to illustrate important elements as they are described.