Abstract
BackgroundLanguage bias is a form of publication bias and constitutes a serious threat to meta-analyses. The Cochrane Controlled Trials Register is one attempt to remedy this and now contains more than 300,000 citations. However we are still unsure if it provides comprehensive coverage, particularly for non-English trials.MethodsWe have recently established a comprehensive register of Japanese trials of psychotropic drugs through extensive personal contacts, electronic searches and handsearches. We examined two Cochrane psychiatry group registers against this Japanese database.ResultsThe Japanese register contained 56 reports of randomized controlled trials (RCTs) of antidepressants for depression but the Cochrane Depression, Anxiety and Neurosis group register contained 18, with an overlap of only nine. The Japanese register contained 61 reports of RCTs of neuroleptics for schizophrenia and the Cochrane Schizophrenia group register contained 36, with an overlap of only six. Taking account of some duplicate publications, only a quarter to a third of all relevant Japanese RCTs were retrievable from the Cochrane group registers.ConclusionsSimilar, or worse, yields may be expected with RCTs conducted in other East Asian countries, and in other fields of medicine. What evidence there is suggests that this situation may lead to a systematic over estimate of treatment effect.
Highlights
Language bias is a form of publication bias and constitutes a serious threat to metaanalyses
We have recently established a comprehensive register of Japanese trials of psychotropic drugs
We requested all the pharmaceutical companies marketing a psychotropic drug in Japan (n = 20) to provide them with the references concerning their randomized controlled trials (RCTs) with Japanese participants
Summary
Language bias is a form of publication bias and constitutes a serious threat to metaanalyses. A particular form of publication bias is the so-called language bias, by which randomised controlled trials (RCTs) with greater estimates of effect size tend to be published in English rather than in the original authors' native languages [1] This bias is compounded by Anglophone databases and journals considerably under representing the totality of RCTs. For example, more than half of trials published in a Hungarian journal, identified through a cover-to-cover hand search, were not reported in MEDLINE [2]. Two notable examples are the Medical Editors Trial Amnesty [5] and the Cochrane Controlled Trials Register (CCTR) The latter contains more than 300,000 citations. We examined how successful the Cochrane psychiatry groups have been in identifying trials conducted in Japan and reported in Japanese by comparing the yields of the groups' specialized registers against this recently created "gold standard."
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