Item response theory and the assumption of unidimensionality for language tests

Abstract

Considerable controversy has arisen around the assumption of unidimen sionality underlying the application of latent trait models of measurement. The intent of the present paper is to provide a clearer articulation of the unidimensionality assumption and to investigate the robustness and appli cability of a particular unidimensional model, the Rasch Model, for use with language proficiency tests that consist of batteries of subtests in a variety of skill areas and that are applied in the testing of the abilities of students from diverse educational, linguistic and cultural backgrounds. Results of the analysis of response data from the administration of a 150- item, five-subskill ESL proficiency/placement examination to 312 entering university students indicated that unidimensionality constraints were not violated.