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. 2018 Jul 27;4(1):e000405. doi: 10.1136/bmjsem-2018-000405

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© Author(s) (or their employer(s)) 2018. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.

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PRISMA flowchart of studies included in meta-analysis. PRISMA, Preferred Reporting Items for Systematic Reviews and Meta-Analysis.