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. 2018 Apr 9;4(1):e000301. doi: 10.1136/bmjsem-2017-000301

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Preferred Reporting Items for Systematic Reviews and Meta-Analysis flow diagram. From: Moher D, Liberati A, Tetzlaff J, Altman DG. The PRISMA Group. Preferred items for systematic reviews and meta-analyses: the PRISMA statement. PLoS Med 2009;6(6):e1000097. doi:10.1371/journal.pmed1000097.