As systematic reviews’ limited coverage of the medical literature necessitates decision-making based on unsystematic review, we investigated a possible advantage of systematic review (aside from dataset size and systematic analysis): does systematic review avoid potential bias in sampling primary studies from high impact factor journals? If randomized controlled trials (RCTs) reported in higher-impact journals present different treatment benefits than RCTs reported in lower-impact journals, readers who focus on higher-impact journals for their rapid literature reviews may introduce bias which could be mitigated by complete, systematic sampling. We randomly sampled Cochrane Library (20 July 2005) treatment reviews that measured mortality as a binary outcome, published in English or French, with at least five RCTs with one or more deaths. Our domain-based assessment of risk of bias included funding source, randomness of allocation sequence, blinding, and allocation concealment. The primary analysis employed logistic regression by a generalized linear model with a generalized estimating equation to estimate the association between various factors and publication in a journal with a high journal impact factor (JIF). From the 29 included systematic reviews, 189 RCTs contributed data. However, in the primary analyses comparing RCT results within meta-analyses, there was no statistically significant association: unadjusted odds of greater than 50% mortality protection in high-JIF (> 5) journals were 1.4 (95% CI 0.42, 4.4) and adjusted, 2.5 (95% CI 0.6, 10). Elements of study quality were weakly, inconsistently, and not statistically significantly correlated with journal impact factor. Journal impact factor may have little to no association with study results, or methodological quality, but the evidence is very uncertain.

中文翻译：

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期刊影响因子，试验效应量和方法学质量似乎无关紧要：系统评价和荟萃分析

由于系统评价对医学文献的报道有限，因此需要基于非系统评价进行决策，因此，我们研究了系统评价的可能优势（除了数据集大小和系统分析之外）：系统评价是否避免了从高影响中抽样基础研究的潜在偏见因子期刊？如果影响较大的期刊报道的随机对照试验（RCT）与影响较小的期刊报道的RCT有不同的治疗益处，那么专注于影响较大的期刊以进行快速文献综述的读者可能会引入偏见，可以通过完全，系统地缓解偏见采样。我们随机抽取了Cochrane图书馆（2005年7月20日）的治疗评价，该评价以死亡率作为二元结果，以英语或法语发布，至少有5例RCT发生了一次或多次死亡。我们基于偏见风险的基于领域的评估包括资金来源，分配顺序的随机性，盲目性和分配隐瞒。初步分析采用具有广义估计方程的广义线性模型进行逻辑回归，以估计各种因素与期刊影响因子（JIF）高的期刊中出版物之间的关联。在29篇系统评价中，有189篇RCT提供了数据。但是，在荟萃分析中比较RCT结果的初步分析中，没有统计学上的显着相关性：在高JIF（> 5）期刊中，超过50％死亡率保护的未调整赔率是1.4（95％CI 0.42，4.4）和调整后为2.5（95％CI 0.6、10）。学习质量的要素薄弱，不一致，并且与期刊影响因子在统计上没有显着相关性。期刊影响因子可能与研究结果或方法学质量几乎没有关联，但证据非常不确定。