Objective To compare cancer-related systematic reviews (SRs) published in the Cochrane Database of SRs (CDSR) and high-impact journals, with respect to type, content, quality and citation rates.
Design Methodological SR with assessment and comparison of SRs and meta-analyses. Two authors independently assessed methodological quality using an Assessment of Multiple Systematic Reviews (AMSTAR)-based extraction form. Both authors independently screened search results, extracted content-relevant characteristics and retrieved citation numbers of the included reviews using the Clarivate Analytics Web of Science database.
Data sources Cancer-related SRs were retrieved from the CDSR, as well as from the 10 journals which publish oncological SRs and had the highest impact factors, using a comprehensive search in both the CDSR and MEDLINE.
Eligibility criteria for selecting studies We included all cancer-related SRs and meta-analyses published from January 2011 to May 2016. Methodological SRs were excluded.
Results We included 346 applicable Cochrane reviews and 215 SRs from high-impact journals. Cochrane reviews consistently met more individual AMSTAR criteria, notably with regard to an a priori design (risk ratio (RR) 3.89; 95% CI 3.10 to 4.88), inclusion of the grey literature and trial registries (RR 3.52; 95% CI 2.84 to 4.37) in their searches, and the reporting of excluded studies (RR 8.80; 95% CI 6.06 to 12.78). Cochrane reviews were less likely to address questions of prognosis (RR 0.04; 95% CI 0.02 to 0.09), use individual patient data (RR 0.03; 95% CI 0.01 to 0.09) or be based on non-randomised controlled trials (RR 0.04; 95% CI 0.02 to 0.09). Citation rates of Cochrane reviews were notably lower than those for high-impact journals (Cochrane reviews: mean number of citations 6.52 (range 0–143); high-impact journal SRs: 74.45 (0–652)).
Conclusions When comparing cancer-related SRs published in the CDSR versus those published in high-impact medical journals, Cochrane reviews were consistently of higher methodological quality, but cited less frequently.
- methodological systematic review
- quality assessment
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Contributors MG designed the data collection tools and analysis, selected studies, analysed and extracted data, and drafted and revised the paper. VMN designed the data collection tools and analysis, selected studies, analysed and extracted data, and drafted and revised the paper. AW extracted and analysed the data and revised the paper. PD initiated the project, designed the data collection tools and analysis, selected studies, monitored data collection and analysis, and revised the paper. NS initiated the project, designed the data collection tools and analysis, selected studies, monitored data collection and analysis, and revised the paper. All authors approved the final version of the article.
Funding Two authors received travel grants by Cochrane to attend and present data at the 23rd Cochrane Colloquium in Seoul, 2016. This research received no other specific grant from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests MG, AW and NS are part of Cochrane Haematological Malignancies, PD is part of Cochrane Urology.
Patient consent Not required.
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement No additional data available.
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