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PRISMA flow diagram outlining the study selection process. From: Moher D, Llberati A, Tetzlatf J, Altman DG, The PRISMA Group (2009). Preferred Reporting items for Systematic Reviews and Meta-Analyses: The PRISMA Statement. Plos Med 6(7): e1000097. 10.1371/journal.pmed1000097. For more information, visit http://www.prisma-statement.org
