Review: Symptoms, Neurocognition and Functional Outcome in Schizophrenia:A Meta-analysis

The paper reviewed here is ‘Symptoms as mediators of the relationship between neurocognition and functional outcome in schizophrenia:A Meta-analysis’ by Joseph Ventura and colleagues. In the conclusion to the abstract the authors write that

‘Although neurocognition and negative symptoms are both predictors of functional outcome, negative symptoms might at least partially mediate the relationship between neurocognition and outcome‘

The authors begin with an introduction in with a discussion of the literature on cognition in relation to negative symptoms. They state their hypothesis thus

‘that the meta-analysis would support a mediation hypothesis for negative symptoms based on the strength of the relationship between neurocognition and negative symptoms, and negative symptoms and outcome‘

The authors detail the methodology. There are 12 search terms that they used in the specified databases which included pubmed and Psycinfo. These 12 search terms did not include IQ or components of standardised test batteries. They did include terms such as executive function and working memory. They also manually extracted further references from retrieved articles. They retrieved 200 articles and further analysed these according to inclusion criteria. Thus diagnoses should be specified in the papers according to DSM criterion which thus excludes those papers which use ICD-10 criteria. I thought the other inclusion criteria seemed to me to be quite sensible and pragmatic e.g. the data in papers should not have been published previously elsewhere.

The authors state their definition of neurocognition and also their use of the MATRICS initiative for structuring domains of cognitive functioning to be used in the analysis and these are ‘speed of processing, attention/vigilance, working memory, verbal learning, visual learning, and reasoning and problem solving’. They excluded social cognition which they thought to be another important independent mediator of the relationship in question. PANSS, SANS and SAPS were used for the assessment of positive and negative symptoms while functional outcome was divided into three broad areas which in turn had a range of outcome measures.

I didn’t understand the next stage. The authors aggregated the data from the neurocognitive domains into a single measure of neurocognition. I didn’t understand how aggregating speed of processing and problem solving for instance was meaningful. Each of these has been identified as a separate domain and so not only is data is being lost in this aggregation. However as the authors hint at in their discussion, not all of these domains are simply defined but are products of inter-related systems – different domains may share neural substrates. Thus if these domains are not entirely separate then I would argue that an additive operation is being applied to dependent data and that the result is not meaningful. I expected that individual test results would be aggregated and that after correcting for multiple comparisons effect sizes with p-values would be identified for the individual tests. While this would produce a large number of different results, these could be grouped after the initial analysis into broader categories if necessary.

The authors have identified a large number of studies according to clearly specified criteria and listed these in the paper together with a brief summary of each paper. The authors have aggregated the data into a single neurocognitive score which I didn’t understand. I would be interested to see an analysis of the interaction between individual test scores and the relationship between negative symptoms and functional outcome.

References

Ventura J, Hellemann G S, Thames A D et al. Symptoms as mediators of the relationship between neurocognition and functional outcome in schizophrenia: A meta-analysis. Schizophrenia Research. 113. 2009. 189-199.

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