OBJECTIVE: The authors' goals are to use scales from the MMPI
hypothesized in their previous research to be correlates of liability to
schizophrenia to differentiate DSM-III schizophrenia from bipolar and
unipolar affective illness and to cross-validate these correlates in an
independently ascertained sample of patients with Research Diagnostic
Criteria (RDC) schizophrenia or affective disorder. METHOD: The criterion
sample consisted of 83 patients consecutively admitted to a state-operated
community mental health center. Diagnosis of schizophrenia; bipolar
disorder, manic; and major depression were assigned by using DSM-III. The
replication sample consisted of 60 adults with RDC diagnoses of
schizophrenia, schizoaffective disorder, bipolar disorder, and unipolar
disorder who were parents of children in two samples collected for a study
of offspring at high risk for schizophrenia and other psychopathology.
After the patients in the criterion sample were classified by logistic
regression analysis, the results were used to classify patients in the
replication sample. RESULTS: The MMPI indicators had adequate sensitivity,
specificity, and predictive power for classifying schizophrenia, and there
was a moderately high rate of diagnostic agreement between the MMPI and
DSM- III. Cross-validation in the replication sample was successful.
Overall, the MMPI index was an adequate inclusion and exclusion criterion
not only for DSM-III-defined but also for RDC-defined schizophrenia.
CONCLUSIONS: A psychometric index composed of the paranoid schizophrenia,
psychoticism, and manifest hostility scales from the MMPI would be a
cost-effective measure to increase diagnostic efficacy in future
schizophrenia research and clinical practice.