BackgroundSystematic reviews (SRs) can help decision makers interpret the deluge of published biomedical literature. However, a SR may be of limited use if the methods used to conduct the SR are flawed, and reporting of the SR is incomplete. To our knowledge, since 2004 there has been no cross-sectional study of the prevalence, focus, and completeness of reporting of SRs across different specialties. Therefore, the aim of our study was to investigate the epidemiological and reporting characteristics of a more recent cross-section of SRs.Methods and FindingsWe searched MEDLINE to identify potentially eligible SRs indexed during the month of February 2014. Citations were screened using prespecified eligibility criteria. Epidemiological and reporting characteristics of a random sample of 300 SRs were extracted by one reviewer, with a 10% sample extracted in duplicate. We compared characteristics of Cochrane versus non-Cochrane reviews, and the 2014 sample of SRs versus a 2004 sample of SRs. We identified 682 SRs, suggesting that more than 8,000 SRs are being indexed in MEDLINE annually, corresponding to a 3-fold increase over the last decade. The majority of SRs addressed a therapeutic question and were conducted by authors based in China, the UK, or the US; they included a median of 15 studies involving 2,072 participants. Meta-analysis was performed in 63% of SRs, mostly using standard pairwise methods. Study risk of bias/quality assessment was performed in 70% of SRs but was rarely incorporated into the analysis (16%). Few SRs (7%) searched sources of unpublished data, and the risk of publication bias was considered in less than half of SRs. Reporting quality was highly variable; at least a third of SRs did not report use of a SR protocol, eligibility criteria relating to publication status, years of coverage of the search, a full Boolean search logic for at least one database, methods for data extraction, methods for study risk of bias assessment, a primary outcome, an abstract conclusion that incorporated study limitations, or the funding source of the SR. Cochrane SRs, which accounted for 15% of the sample, had more complete reporting than all other types of SRs. Reporting has generally improved since 2004, but remains suboptimal for many characteristics.ConclusionsAn increasing number of SRs are being published, and many are poorly conducted and reported. Strategies are needed to help reduce this avoidable waste in research.

Overviews synthesising the results of multiple systematic reviews help inform evidence‐based clinical practice. In this first of two companion papers, we evaluate the bibliometrics of overviews, including their prevalence and factors affecting citation rates and journal impact factor (JIF). We searched MEDLINE, Epistemonikos and Cochrane Database of Systematic Reviews (CDSR). We included overviews that: (a) synthesised reviews, (b) conducted a systematic search, (c) had a methods section and (d) examined a healthcare intervention. Multivariable regression was conducted to determine the association between citation density, JIF and six predictor variables. We found 1218 overviews published from 2000 to 2020; the majority (73%) were published in the most recent 5‐year period. We extracted a selection of these overviews (n = 541; 44%) dated from 2000 to 2018. The 541 overviews were published in 307 journals; CDSR (8%), PLOS ONE (3%) and Sao Paulo Medical Journal (2%) were the most prevalent. The majority (70%) were published in journals with impact factors between 0.05 and 3.97. We found a mean citation count of 10 overviews per year, published in journals with a mean JIF of 4.4. In multivariable analysis, overviews with a high number of citations and JIFs had more authors, larger sample sizes, were open access and reported the funding source. An eightfold increase in the number of overviews was found between 2009 and 2020. We identified 332 overviews published in 2020, which is equivalent to one overview published per day. Overviews perform above average for the journals in which they publish.

BackgroundSelective reporting bias (SRB), the incomplete publication of outcomes measured or of analyses performed in a study, may lead to the over- or underestimation of treatment effects or harms. Cochrane systematic reviews of interventions are required to assess the risk of SRB, achieved in part by applying the Cochrane risk of bias tool to each included randomised trial. The Cochrane Handbook outlines strategies for a comprehensive risk of bias assessment, but the extent to which these are followed by Cochrane review groups (CRGs) has not been assessed to date. The objective of this study was to determine the methods which CRGs require of their authors to address SRB within systematic reviews, and how SRB risk assessments are verified.MethodsA cross-sectional survey was developed and distributed electronically to the 52 CRGs involved in intervention reviews.ResultsResponses from 42 CRGs show that the majority refer their authors to the Cochrane Handbook for specific instruction regarding assessments of SRB. The handbook strategies remain variably enforced, with 57 % (24/42) of CRGs not requiring review authors to search for included trial protocols and 31 % (13/42) not requiring that contact with individual study authors be attempted. Only half (48 %, 20/42) of the groups consistently verify review authors’ assessments of the risk of SRB to ensure completeness.ConclusionsA range of practices are used by CRGs for addressing SRB, with many steps outlined in the Cochrane Handbook being encouraged but not required. The majority of CRGs do not consider their review authors to be sufficiently competent to assess for SRB, yet risk of bias assessments are not always verified by editors before publication. The implications of SRB may not be fully appreciated by all CRGs, and resolving the identified issues may require an approach targeting several steps in the systematic review process.Electronic supplementary materialThe online version of this article (doi:10.1186/s13643-015-0070-y) contains supplementary material, which is available to authorized users.

BackgroundMultiple 'overviews of reviews' conducted on the same topic ("overlapping overviews") represent a waste of research resources and can confuse clinicians making decisions amongst competing treatments. We aimed to assess the frequency and characteristics of overlapping overviews. MethodsMEDLINE, Epistemonikos and Cochrane Database of Systematic Reviews were searched for overviews that: synthesised reviews of health interventions and conducted systematic searches. Overlap was de ned as: duplication of PICO eligibility criteria, and not reported as an update nor a replication. We categorized overview topics according to 22 WHO ICD-10 medical classi cations, overviews as broad or narrow in scope, and overlap as identical, nearly identical, partial, or subsumed. Subsummation was de ned as when broad overviews subsumed the populations, interventions and at least one outcome of another overview. ResultsOf 541 overviews included, 169 (31%) overlapped across similar PICO, fell within 13 WHO ICD-10 medical classi cations, and 62 topics. 148/169 (88%) overlapping overviews were broad in scope. Fifteen overviews were classi ed as having nearly identical overlap (9%); 123 partial overlap (73%), and 31 subsumed (18%) others. ConclusionsOne third of overviews overlapped in content and a majority covered broad topic areas. A multiplicity of overviews on the same topic adds to the ongoing waste of research resources, time and effort across medical disciplines. Authors of overviews can use this study and the sample of overviews to identify gaps in the evidence for future analysis, and topics that are already studied which do not need to be duplicated. HighlightsThis is the rst study to examine overlap across a sample of overviews of reviews.Of 541 overviews published from 2000 to 2018, 169 (31%) were considered overlapping in topic with one or more overviews.

Background: Overviews synthesizing the results of multiple systematic reviews help inform evidence-based clinical practice. In this first of two companion papers, we evaluate the bibliometrics of ‘overviews of systematic reviews’, including their prevalence, number of citations, and factors affecting citation rates and journal impact factor.Methods: We searched MEDLINE, Epistemonikos and the Cochrane library databases. We applied eligibility criteria to identify overviews that: (a) aimed to focus on synthesizing reviews, (b) conducted a systematic search, (c) had a full methods section, and (d) examined a health intervention or clinical treatment effect. A multivariate regression was conducted to determine the association between citation density and impact factor and 6 predictor variables of interest. Results: We found 1218 overviews published from 2000 to 2020; the majority (73%) of which were published in the most recent 5-year period (2016-2020). We extracted a selection of these overviews (n=541; 44%) dated from 2000 to 2018. The 541 overviews were published in 307 journals; the Cochrane Database of Systematic Reviews (8%), PLOS ONE (3%) and the Sao Paulo Medical Journal (2%) being the most prevalent. The majority of overviews (70%) were published in journals with impact factors between 0.05 and 3.97. The average citation rate was 90 (SD ±219.7) over 9 years, or 10 citations per overview per year. In multivariate analysis, overviews with a high number of citations and high journal impact factors tended to have more authors, larger sample sizes, be open access and report funding source. Conclusions: We found an 8 fold increase in the number of overviews from 2009 to 2020; and a representation of one published a day in 2020. Factors driving the increase in overviews include the exponential increase in the number of systematic reviews, the publication of Cochrane guidance on overview of reviews in 2009 and the subsequent publication of the first Cochrane overview in the same year. Our study found a significantly higher mean citation count of 10 overviews per year, published in journals with a mean impact factor of 4.4. These data indicate that, overall, overviews perform above average for the journals in which they publish. We also found that highly cited overviews in high impact factor journals had group authorship, large sample sizes, were openly accessible, and reported funding source.