BACKGROUND There is broad recognition of the importance of evidence in informing clinical decisions. When information from all studies included in a systematic review ("review") does not contribute to a meta-analysis, decision-makers can be frustrated. Our objectives were to use the field of eyes and vision as a case study and examine the extent to which authors of Cochrane reviews conducted meta-analyses for their review's pre-specified main outcome domain and the reasons that some otherwise eligible studies were not incorporated into meta-analyses. METHODS We examined all completed systematic reviews published by Cochrane Eyes and Vision, as of August 11, 2017. We extracted information about each review's outcomes and, using an algorithm, categorized one outcome as its "main" outcome. We calculated the percentage of included studies incorporated into meta-analyses for any outcome and for the main outcome. We examined reasons for non-inclusion of studies into the meta-analysis for the main outcome. RESULTS We identified 175 completed reviews, of which 125 reviews included two or more studies. Across these 125 reviews, the median proportions of studies incorporated into at least one meta-analysis for any outcome and for the main outcome were 74% (interquartile range [IQR] 0-100%) and 28% (IQR 0-71%), respectively. Fifty-one reviews (41%) could not conduct a meta-analysis for the main outcome, mostly because fewer than two included studies measured the outcome (21/51 reviews) or the specific measurements for the outcome were inconsistent (16/51 reviews). CONCLUSIONS Outcome choice during systematic reviews can lead to few eligible studies included in meta-analyses. Core outcome sets and improved reporting of outcomes can help solve some of these problems.

中文翻译：

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系统评价的结果选择和定义导致纳入荟萃分析的合格研究很少：案例研究。

背景技术人们广泛认识到证据在告知临床决策中的重要性。如果来自系统综述（“综述”）中所有研究的信息均不有助于进行荟萃分析，则决策者可能会感到沮丧。我们的目标是使用眼睛和视觉领域作为案例研究，并检查Cochrane评价作者针对其评价的预先指定的主要结果领域进行了荟萃分析的程度以及未将其他符合条件的研究纳入研究的原因荟萃分析。方法我们审查了截至2017年8月11日Cochrane Eyes and Vision发布的所有已完成的系统评价。我们提取了有关每个评价结果的信息，并使用一种算法将一个结果归类为“主要”结果。我们计算了纳入任何结果和主要结果的荟萃分析的纳入研究的百分比。我们研究了主要研究结果未纳入荟萃分析的原因。结果我们确定了175条完整的评价，其中125条评价包括两项或更多项研究。在这125条评论中，纳入至少一项荟萃分析的任何结果和主要结果的研究中位数比例分别为74％（四分位间距[IQR] 0-100％）和28％（IQR 0-71％） ， 分别。51篇评论（41％）无法对主要结果进行荟萃分析，主要是因为少于两项纳入研究对结果进行了评估（21/51篇评论）或对结果的具体度量不一致（16/51篇评论） ）。结论系统评价过程中的结果选择可能导致荟萃分析中几乎没有合格的研究。核心结果集和改进的结果报告可以帮助解决其中一些问题。