Assessing the Effect of Multidimensionality on IRT True-Score Equating for Subgroups of Examinees.

The dimensionality of one form of the Law School Admission Test (LSAT) was assessed with respect to three ethnic groups of test takers. Whether differences in the ability composite have any noticeable impact on item response theory (IRT) true score equating results for these subgroups (African Americans, Hispanic Americans, and Whites) was also studied. Results obtained with respect to the dimensionality of the LSAT showed that a two-dimensional model, specifying analytical reasoning and logical reasoning plus reading comprehension as two abilities, adequately accounted for the item responses of both African-American and Caucasian test takers, but a more complex model was required for the Hispanic subgroup. Results obtained in this study suggest that African-American and Hispanic-American conversion lines appear to be equivalent to the equating function of the majority Caucasian group as well as to the one derived from the total test-taker population. In other words, the current practice of applying a conversion function obtained from the total population to all test takers, without regard to ethnicity, does not penalize minority group test takers. Five tables and 15 figures present results of the analyses. (Contains 71 references.) (SLD)