Replicated psychometric correlates of schizophrenia

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. Diagnoses 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 regres-sion 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-lll-defined but also for RDC-defined schizophrenia. Conclusions: A psychometric index composed of the paranoid schizophrenia, psychoticism, and manifest hostility scales from the MMP/ would be a cost-effective measure to increase diagnostic efficiency in future schizophrenia research and clinical practice.