Evidence from a metaanalysis of randomized controlled trials

Meta-analysis can be defined as 'the quantitative synthesis of the results of systematic overviews of previous studies'. Systematic overviews, in turn, are methods of collating and synthesizing all the available evidence on a particular scientific question. (43) Since randomized controlled trials are often considered to produce the most sophisticated evidence on the efficacy of medical treatments, a meta-analysis conducted on well-selected and relevant randomized controlled trials can be seen as the highest order of knowledge. It follows that the quality of systematic overviews is limited by the quality and quantity of the contributory trials (see A href="ch0007_006.htm#TT06">Table 6).(44) Meta-analysis is described in Chapter.6.1,,,1,,,.2,

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Table B Characteristics of systematic overviews

Cochrane was the first to emphasize the need to bring together, within specific categories, the results of randomized controlled trials. (45> This approach is now central to evidence-based medicine.(4 47 and 48) Within psychiatric evaluation the first meta-analyses were conducted in the late 1970s, and until recently the technique was more often applied to case-control studies than to randomized controlled trials. (43)

Meta-analyses may miss negative trials, since these are often unreported. Another criticism is that large randomized trials do not always agree with a prior meta-analysis. Moreover, neither individual trials not meta-analyses, reporting as they do on population effects, tell us how to treat the individual patient. Despite these criticisms, the strengths of meta-analyses outweigh their weaknesses, although the latter must not be ignored. (49>

An illustration of such an exercise is the systematic overview and meta-analysis conducted by Tyrer et al.,(50) in which they reviewed randomized studies comparing the outcomes of community mental health teams with those of standard care for patients with severe mental illness and disordered personalities. They found 1200 citations using the search strategy: 70 appeared relevant to the review, but only four studies satisfied the inclusion criteria. These four studies included in this review were reported in 12 journal articles, all published in peer-review journals.

The main results of this systematic review are that community mental health team management is associated with fewer deaths by suicide, with fewer people being dissatisfied with services or leaving the studies early. No clear difference was found in admission rates, overall clinical outcomes, or in the duration of inpatient hospital treatment. The authors concluded that community mental health team management is not inferior to non-team standard care in any important respects, and is superior in promoting greater acceptance of treatment. It may also be superior in reducing hospital admissions and avoiding deaths by suicide.

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