Comparability of MMPI and MMPI-2 Profile Patterns: Ben-Porath and Tellegen's Inappropriate Invocation of Mahalanobis's D² Function

Abstract

Ben-Porath and Tellegen (1995) claimed that the data in the article by Humphrey and Dahlstrom (1995) were improperly analyzed by means of Q correlations between raw scores earned by the individuals in the forensic sample to establish pattern comparability between the original Minnesota Multiphasic Personality Inventory (MMPI; Hathaway & McKinley, 1943) and the Minnesota Multiphasic Personality Inventory-2 (MMPI-2; Butcher, Dahlstrom, Graham, Tellegen, & Kaemmer, 1989), which were then contrasted with Q correlations between the corresponding T-score patterns. Ben-Porath and Tellegen (1995) contended that the Q correlation is affected by random factors and that a generalized distance function, D², is the only legitimate index of profile comparability. Data are presented here to show that the Q correlation serves as a reliable index of pattern comparability, relatively unaffected by differences in profile elevation. The Mahalanobis (1936) D² index is too heavily weighted with differences in profile elevation serve as the proper index of equivalence in profile patterning. The findings in the Humphrey and Dahlstrom (1995) article were based on appropriate data-analytic procedures because the primary concern is their investigation was the extent to which the patterns of T-score profiles from the original MMPI and the MMPI-2 are comparable when the raw-score patterns are virtually identical.