Abstract
For the six available sets of empirical data, the discrimination (slope) parameter of the logistic item characteristic curve was found to have a significant positive correlation over items with the difficulty (location) parameter. This unpleasant situation can be eliminated by a suitably chosen transformation of the ability scale. An example of the transformation is given and some empirical results of using the transformed scale are shown.
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References
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Research reported in this paper has been supported by grant GB-41999 from the National Science Foundation.
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Lord, F.M. The ‘ability’ scale in item characteristic curve theory. Psychometrika 40, 205–217 (1975). https://doi.org/10.1007/BF02291567
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DOI: https://doi.org/10.1007/BF02291567