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An Extension of the Rasch Model for Ratings Providing Both Location and Dispersion Parameters

Published online by Cambridge University Press:  01 January 2025

David Andrich
David Andrich*
Affiliation:
The University of Western Australia
*
Requests for reprints should be sent to Dr. David Andrich, Department of Education, The University of Western Australia, NEDLANDS, Western Australia 6009.
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Abstract

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 characterising location and one characterising dispersion. The later parameter, derived from the idea of a unit of scale, is also shown to reflect the shape of rating distributions, ranging from unimodal, through uniform, and then to U-shaped distributions. A brief case is made that when a rating distribution is treated as a random error distribution, then the distribution should be unimodal.

Keywords

logistic latent traitGuttman-scalethresholdsordered categories
Type
Notes and Comments
Information
Psychometrika , Volume 47 , Issue 1 , March 1982 , pp. 105 - 113
Copyright
Copyright © 1982 The Psychometric Society

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