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. 2017 Apr 13;27:24. doi: 10.1038/s41533-017-0022-1

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© The Author(s) 2017

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Fig. 2 — Quality assessment of included studies. Percentages represent the percentage of included articles having a high risk (black bar), unclear risk (light grey bar) or low risk (medium-grey bar) of bias for each category in the Cochrane Collaboration’s risk of bias assessment tool