Egger M, Zellweger-Zähner T, Schneider M, Junker C, Lengeler C, Antes G
Department of Social Medicine, University of Bristol, UK.
Lancet. 1997 Aug 2;350(9074):326-9. doi: 10.1016/S0140-6736(97)02419-7.
Some randomised controlled trials (RCTs) done in German-speaking Europe are published in international English-language journals and others in national German-language journals. We assessed whether authors are more likely to report trials with statistically significant results in English than in German.
We studied pairs of RCT reports, matched for first author and time of publication, with one report published in German and the other in English. Pairs were identified from reports round in a manual search of five leading German-language journals and from reports published by the same authors in English found on Medline. Quality of methods and reporting were assessed with two different scales by two investigators who were unaware of authors' identities, affiliations, and other characteristics of trial reports. Main study endpoints were selected by two investigators who were unaware of trial results. Our main outcome was the number of pairs of studies in which the levels of significance (shown by p values) were discordant.
62 eligible pairs of reports were identified but 19 (31%) were excluded because they were duplicate publications. A further three pairs (5%) were excluded because no p values were given. The remaining 40 pairs were analysed. Design characteristics and quality features were similar for reports in both languages. Only 35% of German-language articles, compared with 62% of English-language articles, reported significant (p < 0.05) differences in the main endpoint between study and control groups (p = 0.002 by McNemar's test). Logistic regression showed that the only characteristic that predicted publication in an English-language journal was a significant result. The odds ratio for publication of trials with significant results in English was 3.75 (95% CI 1.25-11.3).
Authors were more likely to publish RCTs in an English-language journal if the results were statistically significant. English language bias may, therefore, be introduced in reviews and meta-analyses if they include only trials reported in English. The effort of the Cochrane Collaboration to identify as many controlled trials as possible, through the manual search of many medical journals published in different languages will help to reduce such bias.
在讲德语的欧洲地区开展的一些随机对照试验（RCT）发表在国际英文期刊上，而其他一些则发表在德国国内的德文期刊上。我们评估了作者用英文而非德文报告具有统计学显著结果的试验的可能性是否更高。
我们研究了RCT报告对，这些报告以第一作者和发表时间进行匹配，一份报告以德文发表，另一份以英文发表。通过手动检索五份主要德文期刊中的报告以及在Medline上找到的同一作者发表的英文报告来确定报告对。由两名不了解作者身份、所属机构及试验报告其他特征的研究人员使用两种不同的量表评估方法质量和报告质量。主要研究终点由两名不了解试验结果的研究人员选定。我们的主要结果是研究对中显著性水平（以p值表示）不一致的对数。
确定了62对符合条件的报告，但19对（31%）因重复发表而被排除。另有3对（5%）因未给出p值而被排除。对其余40对进行了分析。两种语言报告的设计特征和质量特征相似。只有35%的德文文章报告了研究组与对照组之间主要终点存在显著差异（p<0.05），而英文文章的这一比例为62%（McNemar检验，p=0.002）。逻辑回归显示，预测在英文期刊发表的唯一特征是结果具有显著性。结果显著的试验以英文发表的优势比为3.75（95%可信区间1.25 - 11.3）。
如果结果具有统计学显著性，作者更有可能在英文期刊上发表随机对照试验。因此，如果综述和荟萃分析仅纳入英文报告的试验，可能会引入英语语言偏倚。Cochrane协作网通过手动检索多种不同语言出版的医学期刊来尽可能多地识别对照试验的努力将有助于减少这种偏倚。
