Rasch Models for Ordered Polytomous Items

In health sciences, patient-reported outcomes and/or other purposes often require the use of "polytomous" items with more than two ordered responses by categories. This chapter describes the polytomous Rasch models (PRMs) for ordered polytomous items. For each item, all response categories are ordered. The chapter discusses the properties of the PRM and several assumptions that are made in the PRM. It explains how the PRM can be derived from the dichotomous model. The chapter also summarizes the different ways that the Rasch model for polytomous items can be parameterized. The chapter closes with a discussion on distributions derived from Rasch models.