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Overlapping meta-analyses on the same topic: survey of published studies

BMJ 2013; 347 doi: (Published 19 July 2013) Cite this as: BMJ 2013;347:f4501
  1. Konstantinos C Siontis, resident physician1,
  2. Tina Hernandez-Boussard, assistant professor2,
  3. John P A Ioannidis, professor34
  1. 1Department of Medicine and Mayo School of Graduate Medical Education, College of Medicine, Mayo Clinic, Rochester, MN, USA
  2. 2Department of Surgery, Stanford University School of Medicine, Stanford, CA, USA
  3. 3Stanford Prevention Research Center, Department of Medicine and Department of Health Research and Policy, Stanford University School of Medicine, Stanford, CA, USA
  4. 4Department of Statistics, Stanford University School of Humanities and Sciences, Stanford, CA, USA
  1. Correspondence to: J P A Ioannidis jioannid{at}
  • Accepted 9 July 2013


Objective To assess how common it is to have multiple overlapping meta-analyses of randomized trials published on the same topic.

Design Survey of published meta-analyses.

Data sources PubMed.

Study selection and methods Meta-analyses published in 2010 were identified, and 5% of them were randomly selected. We further selected those that included randomized trials and examined effectiveness of any medical intervention. For eligible meta-analyses, we searched for other meta-analyses on the same topic (covering the same comparisons, indications/settings, and outcomes or overlapping subsets of them) published until February 2013.

Results Of 73 eligible meta-analyses published in 2010, 49 (67%) had at least one other overlapping meta-analysis (median two meta-analyses per topic, interquartile range 1-4, maximum 13). In 17 topics at least one author was involved in at least two of the overlapping meta-analyses. No characteristics of the index meta-analyses were associated with the potential for overlapping meta-analyses. Among pairs of overlapping meta-analyses in 20 randomly selected topics, 13 of the more recent meta-analyses did not include any additional outcomes. In three of the four topics with eight or more published meta-analyses, many meta-analyses examined only a subset of the eligible interventions or indications/settings covered by the index meta-analysis. Conversely, for statins in the prevention of atrial fibrillation after cardiac surgery, 11 meta-analyses were published with similar eligibility criteria for interventions and setting: there was still variability on which studies were included, but the results were always similar or even identical across meta-analyses.

Conclusions While some independent replication of meta-analyses by different teams is possibly useful, the overall picture suggests that there is a waste of efforts with many topics covered by multiple overlapping meta-analyses.


  • Contributors: JPAI had the original idea, and all three authors conceived and designed the study. KCS and TH identified the eligible meta-analyses and extracted the relevant data. KCS and JPAI performed the statistical analyses, and all authors interpreted the data. KCS and JPAI wrote the manuscript, and all authors revised it critically for content and approved the final version. JPAI is guarantor.

  • Funding: This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

  • Competing interests: All authors have completed the ICMJE uniform disclosure form at (available on request from the corresponding author) and declare: no support from any organisation for the submitted work; no financial relationships with any organisations that might have an interest in the submitted work in the previous three years; no other relationships or activities that could appear to have influenced the submitted work.

  • Ethical approval: Not required.

  • Data sharing: Datasets are available from the corresponding author.

This is an Open Access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 3.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See:

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