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. 2016 Oct 5;6:34823. doi: 10.1038/srep34823

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Copyright © 2016, The Author(s)

This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/

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Initial searching included 663 studies (209 from Pubmed, 380 from Web of science, 74 from Embase). And through reviewing the abstracts, 28 articles remained. For the further screening of full texts, 11 studies was finally included in our meta-analysis.