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The distinction of positive and negative symptoms in describing schizophrenic patients has become popular. It presupposes that symptoms cluster in two dimensions, fitting together not only theoretically but empirically. Factor analysis of three published studies of 93, 62 and 52 schizophrenic patients and a large pooled sample showed that more than two distinct dimensions are required to categorise symptoms in schizophrenia. This result is consistent across methods and samples, and with previous literature. The added dimensionality resulted from a splitting of the positive symptom domain into more distinct factors.

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Because these dimensions have impressive consistency across studies, future work must examine their relationship to clinically relevant concepts such as prognosis or etiology and examine four different aspects: longitudinal course, neural mechanisms, relationship to treatment, and interrelationships in other pathological conditions.