The dimensionality of schizophrenia concepts in first-episode psychosis.

This study aimed to determine the dimensionality of concepts of schizophrenia using 11 different diagnostic systems, and then to identify the nature of these dimensions by their relationship to a range of signs and symptoms. The sample consisted of 479 patients admitted with a first episode of functional psychosis. The underlying structure of the 11 diagnostic systems was best represented by an oblique 3-factor solution. Whereas the second and third factors could be meaningfully interpreted by their correlations with signs and symptoms, the first factor, anchored by 'modern' nosologies such as DSM-III-R, was more clearly specified by what it is not (the absence of affective symptoms) rather than by what it is (the presence of characteristic psychotic symptoms). A logistic regression of DSM-III-R diagnosis on to separate diagnostic components supports the contention that duration of illness and affective exclusion criteria discriminate the presence of DSM-III-R schizophrenia much better than the three characteristic psychotic symptom groupings.