A reevaluation of the use of the MMPI in the assessment of combat-related posttraumatic stress disorder.

This study attempts to validate previously developed, empirically based Minnesota Multiphasic Personality Inventory (MMPI) decision rules (Keane, Malloy, & Fairbank, 1984) to aid in the diagnosis of combat-related posttraumatic stress disorder (PTSD). Four groups of 21 subjects each were identified: PTSD, psychotic, depressed, and chronic pain. A decision rule based on the standard clinical scales resulted in a correct classification rate (PTSD vs. non-PTSD) of 81% across the four-group sample. An empirically derived MMPI PTSD scale resulted in a correct classification rate of 77%. However, 43% of the PTSD subjects were incorrectly classified as non-PTSD by these rules. Independent, blind sorting of the 84 MMPI profiles by two doctoral-level clinical psychologists resulted in "hit rates" similar to the MMPI decision rules. The present results suggest that the previously derived, empirically based MMPI decision rules for PTSD do scarcely better than chance on correct classification of individuals with PTSD. We suggest that the differential diagnosis of PTSD is difficult because of the wide variety of symptoms in common with other diagnostic groups, and hence the variability of PTSD subjects on psychometric measures. We also suggest that the MMPI decision rules of Keane et al. (1984) may have utility in identifying subgroup(s) of combat-related PTSDs.