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. 2019 Apr 1;9(4):e025091. doi: 10.1136/bmjopen-2018-025091

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© Author(s) (or their employer(s)) 2019. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.

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Systematic review and meta-analysis flow diagram. All database and grey literature search was performed on 13 October 2017.