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PRISMA flow chart of study inclusion. *Three literature searches were conducted (a search per research question), as shown in the identification box. Next, duplicates were removed from within each search, before being removed by cross‐checking between the searches. **One duplicate was removed from the studies that were finally included. From: Moher, Liberati, Tetzlaff, and Altman (2009). For more information, visit www.prisma-statement.org
