Nutrition and Translational Research in Metabolism (School NUTRIM), Maastricht University, Maastricht, The Netherlands.
Department of Epidemiology and Biostatistics, Amsterdam University Medical Centers, Amsterdam, The Netherlands.
Syst Rev. 2019 Jul 17;8(1):174. doi: 10.1186/s13643-019-1082-9.
Research articles tend to focus on positive findings in their abstract, especially if multiple outcomes have been studied. At the same time, search queries in databases are generally limited to the abstract, title and keywords fields of an article. Negative findings are therefore less likely to be detected by systematic searches and to appear in systematic reviews. We aim to assess the occurrence of this 'abstract reporting bias' and quantify its impact in the literature on the association between diesel exhaust exposure (DEE) and bladder cancer.
We set up a broad search query related to DEE and cancer in general. Full-texts of the articles identified in the search output were manually scanned. Articles were included if they reported, anywhere in the full-text, the association between DEE and bladder cancer. We assume that the use of a broad search query and manual full-text scanning allowed us to catch all the relevant articles, including those in which bladder cancer was not mentioned in the abstract, title or keywords.
We identified 28 articles. Only 12 of these (43%) had mentioned bladder in their abstract, title or keywords. A meta-analysis based on these 12 detectable articles yielded a pooled risk estimate of 1.10 (95% confidence interval [CI] 0.97-1.25), whereas the meta-analysis based on all 28 articles yielded a pooled estimate of 1.03 (95% CI 0.96-1.11).
This case study on abstract reporting bias shows that (a) more than half of all relevant articles were missed by a conventional search query and (b) this led to an overestimation of the pooled effect. Detection of articles will be improved if all studied exposure and outcome variables are reported in the keywords. The restriction on the maximum number of keywords should be lifted.
研究文章往往在摘要中重点关注阳性发现，尤其是在研究了多个结果的情况下。与此同时，数据库中的检索查询通常仅限于文章的摘要、标题和关键词字段。因此，阴性发现不太可能通过系统检索检测到，也不太可能出现在系统评价中。我们旨在评估这种“摘要报告偏倚”的发生情况，并量化其对关于柴油废气暴露（DEE）与膀胱癌之间关联的文献的影响。
我们设置了一个与 DEE 和一般癌症相关的广泛搜索查询。手动扫描搜索结果中确定的文章全文。如果文章在全文的任何地方报告了 DEE 与膀胱癌之间的关联，则将其纳入。我们假设使用广泛的搜索查询和手动全文扫描使我们能够捕捉到所有相关文章，包括那些在摘要、标题或关键词中未提及膀胱癌的文章。
我们确定了 28 篇文章。其中只有 12 篇（43%）在摘要、标题或关键词中提到了膀胱。基于这 12 篇可检测文章的荟萃分析得出的合并风险估计值为 1.10（95%置信区间 [CI] 0.97-1.25），而基于所有 28 篇文章的荟萃分析得出的合并估计值为 1.03（95%CI 0.96-1.11）。
本案例研究表明，（a）超过一半的相关文章被传统的搜索查询遗漏，（b）这导致了合并效应的高估。如果所有研究的暴露和结局变量都在关键词中报告，那么对文章的检测将得到改善。应该取消对关键词数量的限制。
