. 2019 Jul 30;14(7):e0220533. doi: 10.1371/journal.pone.0220533
© 2019 Zhao 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 credited.
Fig 1. Flow diagram of the literature search.
