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Conditions for rasch-dichotomizability of the unidimensional polytomous rasch model

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Abstract

Jansen and Roskam (1986) discussed the compatibility of the unidimensional polytomous Rasch model with dichotomization of the response continuum. They derived a rather strict condition in which dichotomization of multicategory data that fit the unidimensional polytomous Rasch model, results in dichotomous data which fit the dichotomous Research model with effectively the same subject parameter. In this paper a more general dichotomization condition is derived for the polytomous Rasch model, which appears less restrictive, but upholds that the intrinsic logic of the unidimensional polytomous Rasch model defies dichotomization in general. The robustness of dichotomous analysis investigated in a simulation study. It shows a close relation with the two-parameters (Birnbaum) model. Theoretical and methodological implications are discussed.

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Authors and Affiliations

  1. Nijmegen Institutefor Cognition and Information (nici) Division of Mathematical Models, University of Nijmegen, Netherlands

    Edward E. Roskam

  2. Industrial Psychology Branch, The Netherlands Telecommunications Services, The Hague

    Paul G. W. Jansen

Authors
  1. Edward E. Roskam
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  2. Paul G. W. Jansen
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Additional information

The authors are indebted to H. Müller (personal communication, August 1986), for giving an example which pointed toward the core equation in this paper. The authors also acknowledge the critical comments of Th. Bezambinder and P. Wakker, and of Psychometrika's reviewers to an earlier version of this paper.

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Roskam, E.E., Jansen, P.G.W. Conditions for rasch-dichotomizability of the unidimensional polytomous rasch model. Psychometrika 54, 317–332 (1989). https://doi.org/10.1007/BF02294523

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  • DOI: https://doi.org/10.1007/BF02294523

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