Abstract:
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.