Rasch models are characterised by sufficient statistics for all parameters. In the Rasch unidimensional model for two ordered categories, the parameterisation of the person and item is symmetrical and it is readily established that the total scores of a person and item are sufficient statistics for their respective parameters. In contrast, in the…

This book discusses adapting pencil-and-paper tests to computerized testing. Mention is made of models for graded responses to items and of possibilities beyond pencil-and-paper-tests, but the book is essentially about dichotomously scored test items. Contrasts between item response theory and classical test theory are described. (SLD)

An elaboration of a psychometric model for rated data, which belongs to the class of Rasch models, is shown to provide a model with two parameters, one characterizing location and one characterizing dispersion. Characteristics of the dispersion parameter are discussed. (Author/JKS)