Understanding resistance to the data-model relationship in Rasch's paradigm: a reflection for the next generation.

The case for the Rasch models, that The comparison between two stimuli should be independent of which particular individuals were instrumental for the comparison; and vice versa (Rasch, 1961), does not depend on the models accounting for any data set. This has two distinctive consequences on the data-model relationship for the Rasch models. First, and this was recognized by Rasch, when there are deviations of one sort or another, it turns upside down the question of whether it is the model or the test that has gone wrong (Rasch, 1960). Second, because the invariance of comparisons among stimuli, and vice versa, is built into the model rather than being merely a requirement of data, further implications of this requirement can be derived mathematically. These implications, too, inevitably turn some questions, and their solutions, upside down. It is argued that having to look at these implications upside down produces substantial psychological and intellectual resistance amongst those schooled in looking at them in the traditional way. It is also argued that in turning the question upside down, Rasch had an insight that goes beyond the mathematical derivations, and that to sustain this insight requires a paradigm shift (Kuhn, 1970) in the data-model relationship. Using an illustrative example, it is suggested that to maintain this paradigm shift, even by those who research the Rasch models, requires the same uncompromising consistency and passion that Rasch displayed in maintaining faith in his insight.