. 2014 May 15;9(5):e97775. doi: 10.1371/journal.pone.0097775
© 2014 Li et al
This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are properly credited.
Figure 1. Flow diagram of the selection of the studies.
