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Observational Study
. 2024 May 2;13(1):120.
doi: 10.1186/s13643-024-02531-2.

Comparative analysis of Cochrane and non-Cochrane reviews over three decades

Mikkel Zola Andersen  1   2 , Philine Zeinert  3 , Jacob Rosenberg  4   5 , Siv Fonnes  4   5
Affiliations
Observational Study

Comparative analysis of Cochrane and non-Cochrane reviews over three decades

Mikkel Zola Andersen et al. Syst Rev. .

Abstract

Background: Systematic reviews are viewed as the best study design to guide clinical decision-making as they are the least biased publications assuming they are well-conducted and include well-designed studies. Cochrane was initiated in 1993 with an aim of conducting high-quality systematic reviews. We aimed to examine the publication rates of non-Cochrane systematic reviews (henceforth referred to simply as "systematic reviews") and Cochrane reviews produced throughout Cochrane's existence and characterize changes throughout the period.

Methods: This observational study collected data on systematic reviews published between 1993 and 2022 in PubMed. Identified Cochrane reviews were linked to data from the Cochrane Database of Systematic Reviews via their Digital Object Identifier. Systematic reviews and Cochrane reviews were analyzed separately. Two authors screened a random sample of records to validate the overall sample, providing a precision of 98%.

Results: We identified 231,602 (94%) systematic reviews and 15,038 (6%) Cochrane reviews. Publication of systematic reviews has continuously increased with a median yearly increase rate of 26%, while publication of Cochrane reviews has decreased since 2015. From 1993 to 2002, Cochrane reviews constituted 35% of all systematic reviews in PubMed compared with 3.5% in 2013-2022. Systematic reviews consistently had fewer authors than Cochrane reviews, but the number of authors increased over time for both. Chinese first authors conducted 15% and 4% of systematic reviews published from 2013-2022 and 2003-2012, respectively. Most Cochrane reviews had first authors from the UK (36%). The native English-speaking countries the USA, the UK, Canada, and Australia produced a large share of systematic reviews (42%) and Cochrane reviews (62%). The largest publishers of systematic reviews in the last 10 years were gold open access journals.

Conclusions: Publication of systematic reviews is increasing rapidly, while fewer Cochrane reviews have been published through the last decade. Native English-speaking countries produced a large proportion of both types of systematic reviews. Gold open access journals and Chinese first authors dominated the publication of systematic reviews for the past 10 years. More research is warranted examining why fewer Cochrane reviews are being published. Additionally, examining these systematic reviews for research waste metrics may provide a clearer picture of their utility.

Keywords: Bibliometrics; Cochrane; Evidence-based medicine; Information science; Systematic review.

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Conflict of interest statement

Mikkel Zola Andersen reports a relationship with Cochrane Colorectal that includes: employment. Jacob Rosenberg reports a relationship with Cochrane Colorectal that includes: employment. Siv Fonnes reports a relationship with Cochrane Colorectal that includes: employment.

Figures

Fig. 1
Fig. 1
Absolute change in non-Cochrane systematic reviews and Cochrane reviews. Total number (y-axis) of non-Cochrane systematic reviews (light blue) indexed in PubMed and Cochrane reviews (purple) indexed in the Cochrane Database of Systematic Reviews published per year (x-axis) from 1993 to 2022 as absolute number (A) and expressed logarithmically (B)
Fig. 2
Fig. 2
Normalized yearly change of non-Cochrane systematic reviews and Cochrane reviews. Unity-based normalization in a range of [0, 1] of absolute yearly changes in non-Cochrane systematic reviews and Cochrane reviews
Fig. 3
Fig. 3
Country of first authors for non-Cochrane systematic reviews and Cochrane reviews. The plot of the number of publication (y-axis) of Cochrane reviews (A) and non-Cochrane systematic reviews (B) by the top 10 first-author affiliated countries from 1993 to 2022 (x-axis). Analysis was based on 14,614 records (97%) (A) and analysis was based on 207,253 records (89%) (B)
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