Introduction: Extending the Rasch Model

Abstract

The present volume is a collection of chapters on research and development work on extensions of the Rasch model (RM; Rasch, 1960) that have focused on relaxing some fundamental constraints of the original RM, while preserving many of the unique features of the model. More specifically, the volume presents extensions of the RM in which certain homogeneity assumptions on the item level and the population level have been relaxed. With these two types of assumption intact, the original RM decomposes the probability of item responses in two independent components: an item-specific difficulty parameter that is constant across all examinees in the population, and one ability parameter for each examinee that is the same across all items in a given assessment.