Does the Rasch Model Convert an Ordinal Scale into an Interval Scale? Promoting the Rasch Model

Empirical research papers advocating the use of the Rasch model (Rasch, 1960) typically emphasize the unique properties of Rasch measurement, for example, specific objectivity (Rasch, 1977), invariance, sample independence or raw score sufficiency, which are, in fact, closely related. While researchers using factor analytic approaches often downplay the role of specific objectivity or invariance, the scale level of the raw score remains a serious problem in factor analysis. Factor analysis is typically applied to the matrix of Pearson correlations, which require interval-scaled item scores. Therefore, the fact that the Rasch model does not depend on interval-scaled item scores is often put forward as an important property of the model. Often it is explicitly stated that the Rasch mode