. 2016 Mar 8;31(7):940–953. doi: 10.1093/heapol/czw007
© The Author 2016. Published by Oxford University Press in association with The London School of Hygiene and Tropical Medicine.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.
Figure 1.
PRISMA flow diagram.