Symptoms as mediators of the relationship between neurocognition and functional outcome in schizophrenia: A meta-analysis

Background: Neurocognitive functioning in schizophrenia has received considerable attention because of its robust prediction of functional outcome. Psychiatric symptoms, in particular negative symptoms, have also been shown to predict functional outcome, but have garnered much less attention. The high degree of intercorrelation among all of these variables leaves unclear whether neurocognition has a direct effect on functional outcome or whether that relationship to functional outcome is partially mediated by symptoms. Methods: A meta-analysis of 73 published English language studies (total n = 6519) was conducted to determine the magnitude of the relationship between neurocognition and symptoms, and between symptoms and functional outcome. A model was tested in which symptoms mediate the relationship between neurocognition and functional outcome. Functional outcome involved measures of social relationships, school and work functioning, and laboratory assessments of social skill. Results: Although negative symptoms were found to be significantly related to neurocognitive functioning (p < .01) positive symptoms were not (p = .97). The relationship was moderate for negative symptoms (r = -.24, n = 4757, 53 studies), but positive symptoms were not at all related to neurocogniton (r = .00, n = 1297, 25 studies). Negative symptoms were significantly correlated with functional outcome (r = -.42, p < .01), and again the correlation was higher than for positive symptoms (r = -.03, p = 35). Furthermore, our findings support a model in which negative symptoms significantly mediate the relationship between neurocognition and functional outcome (Sobel test p < .01). Conclusions: Although neurocognition and negative symptoms are both predictors of functional outcome, negative symptoms might at least partially mediate the relationship between neurocognition and outcome. (C) 2009 Elsevier B.V. All rights reserved.