Is the partial credit model a Rasch model?

Robert W. Massof

Research output: Contribution to journalArticlepeer-review

5 Scopus citations


A balance scale metaphor is offered as a tool for explaining the principles of measurement and for visualizing the internal structure of dichotomous and polytomous Rasch models. The balance scale metaphor is used to guide the derivation of a general polytomous Rasch model and to illustrate the additional assumptions subsequently required to derive the Andrich (1978) rating scale model (RSM) and the Masters (1982) partial credit model (PCM). The metaphor is used to present the argument that the RSM conforms to the rules of measurement, but the PCM has interactions implicit in its structure that violate specific objectivity and sufficiency of raw scores, which challenge its status as a Rasch model. Using the metaphor and a literal interpretation of the narrative description of the PCM by Masters (1982), a new version of the PCM is derived that does conform to the rules of measurement.

Original languageEnglish (US)
Pages (from-to)114-131
Number of pages18
JournalJournal of applied measurement
Issue number2
StatePublished - 2012
Externally publishedYes

ASJC Scopus subject areas

  • General Medicine


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