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. 2017 Feb 10;14:20. doi: 10.1186/s12966-017-0472-4

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© The Author(s). 2017

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. 1 — Flow diagram of study selection. The diagram illustrates the paper selection process containing number of identified records, included and excluded records, and the reasons why records were excluded. The diagram was adapted from the PRISMA statement [62]