Influences on cognitive heterogeneity in schizophrenia.

A study was conducted of diagnostic reliability, clinical, demographic, iatrogenic, and neurological comorbidity influences on heterogeneity in cognitive function among schizophrenic patients. Comparisons were made between a previously described (Goldstein, 1990) retrospective sample of clinically diagnosed schizophrenic patients and a new sample based on a prospective study of patients meeting strict DSM-III-R diagnostic criteria for schizophrenia. A cluster analysis of a brief battery of cognitive tests suggested a four cluster solution in both samples. The cluster pattern was found to be similar in both samples, indicating that diagnostic unreliability is unlikely to be strongly associated with heterogeneity. Age, general intelligence, and education were found to have significant influences on cluster membership, with length of illness and hospitalization having less robust influences. It was concluded that heterogeneity has a relatively mild relationship with the various influences studied, but a great deal of the diversity in level and pattern of cognitive function found among schizophrenic patients is likely to be a function of heterogeneity within the disorder itself.