German Cochrane Center, Institute of Medical Biometry and Medical Informatics, University Medical Center Freiburg, 79110 Freiburg, Germany.
Syst Rev. 2013 May 2;2:24. doi: 10.1186/2046-4053-2-24.
Meta-analyses are particularly vulnerable to the effects of publication bias. Despite methodologists' best efforts to locate all evidence for a given topic the most comprehensive searches are likely to miss unpublished studies and studies that are published in the gray literature only. If the results of the missing studies differ systematically from the published ones, a meta-analysis will be biased with an inaccurate assessment of the intervention's effects.As part of the OPEN project (http://www.open-project.eu) we will conduct a systematic review with the following objectives:▪ To assess the impact of studies that are not published or published in the gray literature on pooled effect estimates in meta-analyses (quantitative measure).▪ To assess whether the inclusion of unpublished studies or studies published in the gray literature leads to different conclusions in meta-analyses (qualitative measure).
Methodological research projects of a cohort of meta-analyses which compare the effect of the inclusion or exclusion of unpublished studies or studies published in the gray literature.
To identify relevant research projects we will conduct electronic searches in Medline, Embase and The Cochrane Library; check reference lists; and contact experts.
Information will be collected on the area of health care; the number of meta-analyses included in the methodological research project; the number of studies included in the meta-analyses; the number of study participants; the number and type of unpublished studies; studies published in the gray literature and published studies; the sources used to retrieve studies that are unpublished, published in the gray literature, or commercially published; and the validity of the methodological research project.
DATA SYNTHESIS will involve descriptive and statistical summaries of the findings of the included methodological research projects.
Results are expected to be publicly available in the middle of 2013.
荟萃分析特别容易受到发表偏倚的影响。尽管方法学家们尽力寻找给定主题的所有证据，但最全面的搜索仍可能遗漏未发表的研究和仅在灰色文献中发表的研究。如果缺失研究的结果与已发表的结果有系统差异，荟萃分析将存在偏差，对干预效果的评估不准确。作为 OPEN 项目（http://www.open-project.eu）的一部分，我们将进行以下目标的系统评价：
评估未发表或在灰色文献中发表的研究对荟萃分析汇总效应估计的影响（定量衡量）。
评估纳入未发表研究或在灰色文献中发表的研究是否会导致荟萃分析得出不同的结论（定性衡量）。
比较纳入或排除未发表研究或在灰色文献中发表的研究对荟萃分析影响的一系列荟萃分析方法学研究项目。
为了确定相关的研究项目，我们将在 Medline、Embase 和 The Cochrane Library 中进行电子检索；检查参考文献列表；并联系专家。
1）荟萃分析中效应估计值随未发表或在灰色文献中发表的研究的纳入或排除而变化的程度；2）纳入未发表研究对荟萃分析结论的影响程度。
将收集有关医疗保健领域的信息；纳入方法学研究项目的荟萃分析数量；纳入荟萃分析的研究数量；研究参与者数量；未发表研究和发表在灰色文献中的研究的数量和类型；用于检索未发表、发表在灰色文献或商业出版的研究的来源；以及方法学研究项目的有效性。
将对纳入的方法学研究项目的发现进行描述性和统计总结。
预计结果将于 2013 年年中公布。
