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. 2019 Apr 11;5:13. doi: 10.1186/s40798-019-0186-z

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© The Author(s). 2019

Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

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Fig. 1 — Flow chart of study selection according to PRISMA guidelines for reporting systematic reviews and meta-analyses