The Nature of Objectivity with the Rasch Model
Embretson, Susan E.
Dawis, René V.
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Although it has been claimed that the Rasch model leads to a higher degree of objectivity in measurement than has been previously possible, this model has had little impact on test development. Population-invariant item and ability calibrations, together with the statistical equivalency of any two item subsets, are supposedly possible if the item pool has been calibrated by the Rasch model. Initial research has been encouraging, but the implications of underlying assumptions and operational computations in the Rasch model for trait theory have not been clear from previous work. The current paper presents an analysis of the conditions under which the claims of objectivity will be substantiated, with special emphasis on the nature of equivalent forms. It is concluded that the real advantages of the Rasch model will not be apparent until the technology of trait measurement becomes more sophisticated.