Studies are usually identified by searching bibliographic databases such as EMBASE, MEDLINE, or PsycLIT. Hand-searching relevant journals, conference proceedings, and references is also often undertaken.
A systematic review would be a misnomer if the researchers did not make the means of identification of studies clear and reproducible. The exact source of trials, and the search strategies, must be explicit. It is at this point that the advice of an information specialist is important. The coverage of mental health journals in many bibliographic databases is poor and often limited by region or language (2.6) so that searching several sources is advisable.
In recent years, however, the situation for those wishing to identify all treatment trials relevant to a particular topic has become easier. The Cochrane Controlled Trials Register'2!) is the largest and most comprehensive bibliographic database of published and unpublished randomized trials, and controlled clinical studies, in existence. For citations of trials, this specialist register has eclipsed databases such as EMBASE, Medline, and PsycLIT. Searching the Cochrane Controlled Trials Register also avoids the problem of the numerous 'false' positive citations produced by searches of unspecialized biomedical databases.
Identifying every possible study is important. Potent biases operate in this area. Trials that have statistically significant results are more likely to be published than those reporting equivocal findings,(28) and they are more likely to be published in English.(29) Systematic reviews incorporating only Anglophone published data or trials from one region are likely to produce, at best, imprecise, and at worse, overoptimistic views of efficacy.
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