. 2018 May 28;15(6):1092. doi: 10.3390/ijerph15061092
© 2018 by the authors.
Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
Figure 1.
PRISMA diagram of the study selection process.