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Two procedures, one based on item difficulties, the other based on person abilities, were used to equate 14 forms of a reading comprehension test using the Rasch model. These forms had no items in common. For practical purposes, the two procedures produced equivalent results. An advantage of common-person equating for testing the unidimensionality assumption is pointed out, and the need for caution in interpreting tests of common-item invariance is stressed.
Geofferey N. Masters (Fri,) studied this question.