Psychometrika

, Volume 47, Issue 2, pp 149–174 | Cite as

A rasch model for partial credit scoring

  • Geoff N. Masters
Article

Abstract

A unidimensional latent trait model for responses scored in two or more ordered categories is developed. This “Partial Credit” model is a member of the family of latent trait models which share the property of parameter separability and so permit “specifically objective” comparisons of persons and items. The model can be viewed as an extension of Andrich's Rating Scale model to situations in which ordered response alternatives are free to vary in number and structure from item to item. The difference between the parameters in this model and the “category boundaries” in Samejima's Graded Response model is demonstrated. An unconditional maximum likelihood procedure for estimating the model parameters is developed.

Key words

latent trait Rasch model ordered categories partial credit 

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Reference notes

  1. Rasch, G. Objektivitet i samfundsvidenskaberne et metodeproblem. Paper presented at the University of Copenhagen, 1972 (mimeo).Google Scholar
  2. Masters, G. N. A Rasch model for rating scales. Doctoral dissertation, University of Chicago, 1980.Google Scholar
  3. Wright, B. D. & Masters, G. N. The measurement of knowledge and attitude.Research Memorandum No. 30, MESA Psychometric Laboratory, Department of Education, University of Chicago, 1981.Google Scholar
  4. Masters, G. N. & Wright, B. D. A model for partial credit scoring.Research Memorandum No. 31, MESA Psychometric Laboratory, Department of Education, University of Chicago, 1981.Google Scholar

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Copyright information

© The Psychometric Society 1982

Authors and Affiliations

  • Geoff N. Masters
    • 1
  1. 1.Department of EducationUniversity of ChicagoChicago

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