The incremental validity of the MMPI-2: when does therapist access not enhance treatment outcome?

The present study examined whether therapist access to the Minnesota Multiphasic Personality Inventory (MMPI-2) predicted favorable treatment outcome, above and beyond other assessment measures. A manipulated assessment design was used, in which patients were randomly assigned either to a group in which therapists had access to their MMPI-2 data or to a group without therapist access to such information. Illness severity, improvement ratings, number of sessions attended, and premature termination were indicators of therapy outcome. Results indicated that therapist access to the MMPI-2 data did not add to the prediction of positive treatment outcome beyond that predicted by other measures in this setting. Findings from this initial study suggest that, compared with other resources, perhaps in clinical settings with an emphasis on diagnosis-based and evidence-based treatment, the MMPI-2 may not provide incrementally valid information. However, these effects warrant replication across different settings and samples. Guidelines for future studies are discussed.