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. 2016 Aug 8;14:209. doi: 10.1186/s12957-016-0957-7

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© The Author(s). 2016

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. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

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Fig. 2 — a Risk of bias graph: review authors’ judgments about each risk of bias item presented as percentages across all included studies. b Risk of bias summary: review authors’ judgments about each risk of bias item for each included study