The incremental validity of MMPI-2 supplementary scales

Several hundred special or supplementary scales were created for the original Minnesota Multiphasic Personality Inventory (MMPI). At the time of the release of the Minnesota Multiphasic Personality Inventory-e (MMPI-2) in 1989, 15 supplementary scales were included in, or developed for, this revised test. The degree to which the MMPI-P supplementary scales provide either new information or data that are redundant with that already provided by the MMPI-2 basic scales has not been investigated in prior research. The current study examines the incremental validity of the MMPI-2 supplementary scales in a sample of 597 adult psychiatric inpatients using criterion measures composed of other self-report instruments and clinicians' ratings of psychopathology. MMPI-2 basic and supplementary scale data were entered in a series of hierarchical regression analyses to statistically evaluate the degree to which the supplementary scales provided incremental contributions in the predict:ion of valiance on outcome measures. These results were compared with levels of prediction achieved by forced entry of all 13 of the basic scales and with incremental variance produced by the assignment of random T-score values to the supplementary scales. Major findings indicate that the inclusion of supplementary scale data only marginally increased the proportion of variance accounted for in external criterion variables.