Nearly 80 systematic reviews were published each day: Observational study on trends in epidemiology and reporting over the years 2000-2019

Falk Hoffmann; Katharina Allers; Tanja Rombey; Jasmin Helbach; Amrei Hoffmann; Tim Mathes; Dawid Pieper

doi:10.1016/j.jclinepi.2021.05.022

Nearly 80 systematic reviews were published each day: Observational study on trends in epidemiology and reporting over the years 2000-2019

J Clin Epidemiol. 2021 Oct:138:1-11. doi: 10.1016/j.jclinepi.2021.05.022. Epub 2021 Jun 4.

Authors

Falk Hoffmann¹, Katharina Allers², Tanja Rombey³, Jasmin Helbach², Amrei Hoffmann², Tim Mathes⁴, Dawid Pieper⁴

Affiliations

¹ Department of Health Services Research, School of Medicine and Health Sciences, Carl von Ossietzky University Oldenburg, Oldenburg, Germany. Electronic address: falk.hoffmann@uni-oldenburg.de.
² Department of Health Services Research, School of Medicine and Health Sciences, Carl von Ossietzky University Oldenburg, Oldenburg, Germany.
³ Institute for Research in Operative Medicine, Faculty of Health, School of Medicine, Witten/Herdecke University, Cologne, Germany; Department of Health Care Management, Technische Universität Berlin, Berlin, Germany.
⁴ Institute for Research in Operative Medicine, Faculty of Health, School of Medicine, Witten/Herdecke University, Cologne, Germany.

PMID: 34091022
DOI: 10.1016/j.jclinepi.2021.05.022

Abstract

Background: Systematic reviews (SRs) are useful tools in synthesising the available evidence, but high numbers of overlapping SRs are also discussed in the context of research waste. Although it is often claimed that the number of SRs being published is increasing steadily, there are no precise data on that. We aimed to assess trends in the epidemiology and reporting of published SRs over the last 20 years.

Methods: A retrospective observational study was conducted to identify potentially eligible SRs indexed in PubMed from 2000 to 2019. From all 572,871 records retrieved, we drew a simple random sample of 4,000. The PRISMA-P definition of SRs was applied to full texts and only SRs published in English were included. Characteristics were extracted by one reviewer, with a 20% sample verified by a second person.

Results: A total of 1,132 SRs published in 710 different journals were included. The estimated number of SRs indexed in 2000 was 1,432 (95% CI: 547-2,317), 5,013 (95% CI: 3,375-6,650) in 2010 and 29,073 (95% CI: 25,445-32,702) in 2019. Transparent reporting of key items increased over the years. About 7 out of 10 named their article a SR (2000-2004: 41.9% and 2015-2019: 74.4%). In 2000-2004, 32.3% of SRs were based in the UK (0% in China), in 2015-2019 24.0% were from China and 10.8% from the UK. Nearly all articles from China (94.9%) conducted a meta-analysis (overall: 58.9%). Cochrane reviews (n = 84; 7.4%) less often imposed language restrictions, but often did not report the number of records and full texts screened and did not name their article a SR (22.6% vs. 73.4%).

Conclusions: We observed a more than 20-fold increase in the number of SRs indexed over the last 20 years. In 2019, this is equivalent to 80 SRs per day. Over time, SRs got more diverse in respect to journals, type of review, and country of corresponding authors. The high proportion of meta-analyses from China needs further investigation.

Study registration: Open Science Framework (https://osf.io/pxjrv/).

Keywords: Cochrane Review; Evidence-Based Practice; Meta-Analysis; Reporting; Systematic Review; Trends.

Publication types

Observational Study

MeSH terms

Biomedical Research / statistics & numerical data*
Epidemiologic Studies*
Forecasting
Humans
Meta-Analysis as Topic*
Publications / statistics & numerical data*
Publications / trends*
Research Report / trends*
Retrospective Studies
Systematic Reviews as Topic*