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. 2017 Aug 29;7:9813. doi: 10.1038/s41598-017-10230-3

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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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Flow diagram of study selection. Note: A total of 5785 studies was identified through our search of the four electronic databases. After removing 993 duplicates, only 4792 studies were retrieved. After reading the titles and abstracts, only 48 studies remained. A total of 38 articles were excluded after reading the full-text.