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General medicine
Single screening or double screening for study selection in systematic reviews?
  1. Kamal R Mahtani,
  2. Carl Heneghan,
  3. Jeffrey Aronson
  1. Centre for Evidence Based Medicine, Nuffield Department of Primary Care Health Sciences, University of Oxford, Oxford, UK
  1. Correspondence to Dr Kamal R Mahtani, Nuffield Department of Primary Care Health Sciences, University of Oxford, Oxford OX2 6GG, UK; kamal.mahtani{at}

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​Recent systematic reviews provide evidence on the need for more than one reviewer when screening studies for inclusion in systematic reviews.

Why is this important?

Systematic reviews are important tools for the practice of evidence-based healthcare. Part of their value comes from their ability to obtain new knowledge by synthesising existing data. The reliability of this knowledge arises from the review process, which, when implemented correctly, should be predefined, transparent and rigorous.1

Conducting a high-quality systematic review has resource implications, for example, time, size of the research team and costs. A random sample of systematic reviews in the Prospective Register of Systematic Reviews (PROSPERO) showed that the mean estimated time to complete the project and publish the review was 67 weeks (SD=31; range 6–186 weeks); each review needed a mean of 5 team members (SD=3; range 1–27).2 The search for publications, review of abstracts and retrieval and review of selected full-text papers alone can take an average of 332 hours.3 Systematic reviews are not cheap; some estimates suggest that they can cost several hundred thousand pounds.4

The need to balance timeliness of results with rigour has meant that consideration has been given to ways in which the review process could be restricted, for example, by reducing the number of reviewers who screen studies for inclusion …

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  • Twitter @krmahtani, @carlheneghan, @JKAronson

  • Contributors KRM wrote the first draft and all authors contributed to the development of subsequent versions.

  • Funding All authors are supported by the BMJ Evidence Based Medicine journal in their roles as editors. KRM and CH are also supported by the National Institute for Health Research School for Primary Care Research Evidence Synthesis Working Group (project number 390).

  • Competing interests KRM is the director of MSc EBHC (Systematic Reviews) at the University of Oxford. KRM and CH report grants from the NIHR including the NIHR School of Primary Care Research Evidence Synthesis Working Group (project number 390). KRM and JA are associate editors of the BMJ EBM journal. CH is the editor in chief of the BMJ EBM journal.

  • Patient consent for publication Not required.

  • Provenance and peer review Not commissioned; internally peer reviewed.