Using IRT to separate measurement bias from true group differences on homogeneous and heterogeneous scales: an illustration with the MMPI.

The authors present a didactic illustration of how item response theory (IRT) can be used to separate measurement bias from true group differences on homogeneous and heterogeneous scales. Several bias detection methods are illustrated with 12 unidimensional Minnesota Multiphasic Personality Inventory (MMPI) factor scales (Waller, 1999) and the 13 multidimensional MMPI validity and clinical scales. The article begins with a brief review of MMPI bias research and nontechnical reviews of the 2-parameter logistic model (2-PLM) and several IRT-based methods for bias detection. A goal of this article is to demonstrate that homogeneous and heterogeneous scales that are composed of biased items do not necessarily yield biased test scores. To that end, the authors perform differential item- and test-functioning analyses on the MMPI factor, validity, and clinical scales using data from 511 Blacks and 1,277 Whites from the California Youth Authority.