Independence and overlap among neurocognitive correlates of community functioning in schizophrenia

Existing literature on the neurocognitive correlates of community functioning in schizophrenia has not adequately focused on the relationships among the correlated variables. In a sample of 40 outpatients with schizophrenia and related disorders, we studied two sets of variables that we expected to be related to broad ratings of community functioning: (1) the Wechsler Adult Intelligence Scale-III (WAIS-III) index scores for verbal comprehension, perceptual organization, working memory, and processing speed; and (2) positive, negative, disorganized and affective symptom variables. Of the WAIS-III index scores, working memory and processing speed entered a stepwise regression, together accounting for substantial variance in functional ratings (R(2)=0.37). However, only processing speed remained significantly associated with community functioning after controlling for the other indexes. In relation to community functioning, the remaining indexes appeared to be overlapping markers of general cognitive ability, rather than specific measures of discrete cognitive domains. Addition of positive and negative symptom variables in a further analysis greatly increased the explained functional variance (R(2)=0.65). Processing speed overlapped substantially with negative symptoms in predicting functioning, while the other WAIS-III indexes were independent of symptomatology. Results illustrate the importance of (1) knowing which neurocognitive variables have specific relationships to community functioning and which reflect the influence of more general cognitive ability in daily life, and (2) appreciating areas of overlap and independence among classes of correlates of functioning, such as neurocognitive and symptom variables. This improved understanding has implications for predictive models of community functioning, for cognitive rehabilitation and deficit compensation strategies, and for assessment practice.