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. 2017 Nov 14;7:15506. doi: 10.1038/s41598-017-15860-1

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© The Author(s) 2017

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as 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 images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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QUADAS-2 assessment of study quality. Grouped bar charts of the QUADAS-2 scores are expressed as percentage of the 12 included studies meeting each criterion. For each domain, the proportion of the included studies that indicate low/high/unclear concerns of applicability or risk of bias are displayed in light grey = “yes” answers (good quality), dark grey bar = “unclear” answers, and medium bar = “no” answers (low quality).