As recommended by the Cochrane Collaboration [35], two reviewers will assess the strength of evidence of the included studies using the Grades of Recommendation, Assessment, Development, and Evaluation (GRADE) approach [36]. The reviewers will independently rate the quality of each study; disagreements will be resolved through discussion with the senior author. We will also use funnel plots to assess potential publication bias [37].
Copyright and License information: 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. 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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