Abstract

Polytomous item response theory (IRT) has proven fertile ground for psychological measurement model development. While unidimensional dichotomous IRT models primarily come in three basic choices, the measurement practitioner has many more potential models from which to choose when working with polytomous response data, even within the subset of unidimensional models. Ostini and Nering (2006) provide a consideration of some of the ways polytomous IRT models differ as a class from dichotomous models. Nering and Ostini (2010) provide a deeper investigation of the historical and conceptual origins of the most influential models in a collection of chapters written by the researchers most closely associated with the development of the models.