This article focuses on the underlying structure and temporal course of the symptoms of schizophrenia.
Ratings of symptoms in 90 schizophrenic patients were made each month for 10 years following the first hospitalization. The analytic methods consisted of cross-tabulation, dichotomous factor analysis, and bivariate dichotomous time series.
The factor analyses revealed positive and negative factors with a slight tendency to merge over time. The prevalence of positive and negative symptoms declined in the year following first hospitalization and was stable thereafter. Positive and negative symptoms in 1 month were highly predictive of the same type of symptoms in the next month. Neither type of symptom was strongly associated with the other type in the following month when both types were included in the model. The predictability of the process increased with time.
With a few minor caveats, the results suggest that the positive and negative symptom clusters are independent, both cross-sectionally and longitudinally.
Eaton WW, Thara R, Federman B, Melton B, Liang K. Structure and Course of Positive and Negative Symptoms in Schizophrenia. Arch Gen Psychiatry. 1995;52(2):127-134. doi:10.1001/archpsyc.1995.03950140045005