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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Andrich, D. An extension of the rasch model for ratings providing both location and dispersion parameters. Psychometrika 47, 105–113 (1982). https://doi.org/10.1007/BF02293856
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DOI: https://doi.org/10.1007/BF02293856