Objective Covariance among psychiatric disorders can be accounted for by higher-order internalizing, externalizing, and psychosis dimensions, but placement of bipolar disorder within this framework has been inconsistent. Moreover, whether deviations in normal-range personality can explain psychosis and vulnerability to severe mood lability, as seen in schizophrenia and bipolar disorder, remains unclear.
Methods Exploratory factor analysis of interviewer-rated clinical symptoms in patients with schizophrenia or bipolar disorder, their first-degree biological relatives, and nonpsychiatric controls (total N = 193), followed by examination of associations between symptom dimensions and self reports on personality questionnaires.
Results Covariance in symptoms was accounted for by five factors: positive symptoms of psychosis, negative symptoms of psychosis, disorganization, mania, and depression/anxiety. Schizophrenia and bipolar patients/relatives reported elevated negative emotionality and absorption and lower positive emotionality relative to controls. Personality did not differ between schizophrenia and bipolar patients/relatives, but there was a different pattern of associations between symptoms and personality in these groups.
Conclusions Discrete dimensions reflecting psychotic, manic, and depressive symptoms emerge when a broad set of clinical symptoms is examined in a sample overrepresented by psychotic experiences and affective disturbances. Although normal-range personality traits index common phenotypes spanning schizophrenia and bipolar spectra, the same symptoms may carry different significance across disorders.