Department of Health Services Research, School of Medicine and Health Sciences, Carl Von Ossietzky University Oldenburg, Oldenburg, Germany.
Institute for Research in Operative Medicine, Faculty of Health, School of Medicine, Witten/Herdecke University, Cologne, Germany.
BMC Med Res Methodol. 2022 Aug 20;22(1):230. doi: 10.1186/s12874-022-01710-w.
Restrictions in systematic reviews (SRs) can lead to bias and may affect conclusions. Therefore, it is important to report whether and which restrictions were used. This study aims to examine the use of restrictions regarding language, publication period, and study type, as well as the transparency of reporting in SRs of effectiveness.
A retrospective observational study was conducted with a random sample of 535 SRs of effectiveness indexed in PubMed between 2000 and 2019. The use of restrictions and their reporting were analysed using descriptive statistics.
Of the total 535 SRs included, four out of every ten (41.3%) lacked information on at least one of the three restrictions considered (language, publication period, or study type). Overall, 14.6% of SRs did not provide information on restrictions regarding publication period, 19.1% regarding study type, and 18.3% regarding language. Of all included SRs, language was restricted in 46.4%, and in more than half of the SRs with restricted language (130/248), it was unclear whether the restriction was applied during either the search or the screening process, or both. The restrictions were justified for publication period in 22.2% of the respective SRs (33/149), study type in 6.5% (28/433), and language in 3.2% (8/248). Differences in reporting were found between countries as well as between Cochrane and non-Cochrane reviews.
This study suggests that there is a lack of transparency in reporting on restrictions in SRs. Authors as well as editors and reviewers should be encouraged to improve the reporting and justification of restrictions to increase the transparency of SRs.
系统评价（SR）中的限制因素可能会导致偏倚，并影响结论。因此，报告是否以及使用了哪些限制因素非常重要。本研究旨在检查 SR 中关于语言、出版时间和研究类型的限制因素的使用情况，以及报告的透明度。
采用回顾性观察性研究方法，随机抽取 2000 年至 2019 年期间在 PubMed 上索引的 535 篇有效性 SR。使用描述性统计方法分析限制因素的使用情况及其报告情况。
在纳入的 535 篇 SR 中，每十篇中有四篇（41.3%）至少缺乏三种限制因素（语言、出版时间或研究类型）之一的信息。总体而言，14.6%的 SR 未提供关于出版时间限制的信息，19.1%关于研究类型，18.3%关于语言。在所有纳入的 SR 中，有 46.4%对语言进行了限制，在超过一半（130/248）对语言进行限制的 SR 中，不清楚该限制是在检索还是筛选过程中应用的，或者两个过程都应用了。在分别有 33/149 篇 SR 中，22.2%对出版时间限制进行了合理化，6.5%（28/433）对研究类型，3.2%（8/248）对语言限制进行了合理化。在报告方面，发现国家之间以及 Cochrane 和非 Cochrane 评价之间存在差异。
本研究表明，SR 中关于限制因素的报告缺乏透明度。应鼓励作者以及编辑和审稿人改进限制因素的报告和合理化，以提高 SR 的透明度。
