An extension of the rasch model for ratings providing both location and dispersion parameters |
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Authors: | Dr. David Andrich |
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Affiliation: | (1) Department of Education, The University of Western Australia, 6009 NEDLANDS, Western Australia, Australia |
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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. |
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Keywords: | logistic latent trait Guttman-scale thresholds ordered categories |
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