Positive, negative, and disorganisation factors from the Schedule for Affective Disorders and Schizophrenia and the Present State Examination. A three-factor solution.

The use of items from the Schedule for Affective Disorders and Schizophrenia and from the Present State Examination scales for assessing positive and negative symptoms in schizophrenia was examined using factor analysis. The factorial structure of the items which putatively assess positive and negative symptoms was examined. A three-factor solution was obtained with factors identified as: a negative symptom factor (factor 1); a positive symptom factor (factor 2); a 'disorganisation' factor (factor 3), consisting primarily of items related to disordered thinking. A solution which was highly similar in important loadings was obtained with an independent sample of patients. High correlations of the rotated factors with the external criteria supported the interpretations of the factors. The results indicate that symptoms generally classified as negative or positive are factorially independent. Furthermore, a disorganisation factor, consisting of items previously included in positive and negative symptoms factors, is necessary for a full representation of the factor structure.