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. 2014 Aug 27;14:237. doi: 10.1186/s12888-014-0237-4

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© Esch et al.; licensee BioMed Central Ltd. 2014

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. 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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Summary of risk of bias assessment. *Green: At least 2 types of confounding variables, among sociodemographic, family and academic variables. Yellow: One type of confounding variables. Red: 0 type of confounding variables.