PURPOSE: We aimed to evaluate the Minnesota Multiphasic Personality Inventory-2 (MMPI-2) as a potential means of improving on the SCID's diagnostic efficacy.

METHODS: 76 first-admission patients were assigned DSM-IV consensus diagnoses by two experienced psychiatrists using all available information, then dichotomized into non-affective psychosis and other mental illness groups. The patients were also given the SCID and the MMPI-2. The diagnostic performance of the MMPI-2 was compared to that of the SCID to assess both diagnostic accuracy and incremental validity.

RESULTS: MMPI-2 scales 8 (Schizophrenia) and BIZ (Bizarre Mentations) correctly identified 58% and 56% respectively of non-affective psychotic patients. The Goldberg Index had an overall correct classification rate of 70%, but only identified 49% of the psychosis group. The SCID had a correct classification rate of 66% but correctly identified only 25% of the non-affective psychosis patients. Three MMPI-2 scales combined with the SCID resulted in an overall correct classification rate of 73%, and identification of 66% of the non-affective psychosis patients.

CONCLUSION: The results suggest that the MMPI-2 may identify early psychosis at least as well as the SCID. Furthermore, using a combination of the MMPI-2 and the SCID shows incremental validity over using the SCID alone.