Background: Prior studies of common disorders in community-dwelling adults identified internalizing and externalizing spectra of mental illness. We investigated the placement of schizophrenia and schizotypal personality disorder in this framework and tested the validity of the resulting organization in a clinical population.
Methods: The data came from the Suffolk County Mental Health Project cohort (N = 628), which consists of first-admission patients with psychosis recruited from inpatient units throughout Suffolk County, NY (72% response rate). The sample was reassessed multiple times over the following 10 years. Complete diagnostic data were available for 469 participants. Mental health professionals diagnosed 11 target conditions based on semistructured clinical interviews, review of medical records, and reports of significant others. Two validators were included: family history of schizophrenia and 10-year illness course.
Results: Confirmatory factor analysis revealed that the The Diagnostic and Statistical Manual of Mental Disorders-IV grouping of conditions fit the data poorly. The best alternative classification consisted of three clusters: internalizing, externalizing, and schizophrenic. Both validators supported the coherence and distinctiveness of the schizophrenic cluster.
Conclusions: We replicated internalizing and externalizing spectra in a clinical population, identified a schizophrenic spectrum, and provided initial evidence of its validity. These findings suggest that schizotypal personality disorder may be better placed with schizophrenia, antisocial conditions with substance use disorders, and major depression with anxiety disorders.