Received: 16 September 2018
Accepted: 9 July 2019
First Online: 15 July 2019
Ethics approval and consent to participate
: All the data supporting our findings in this paper were freely downloaded from the PubMed, EMBASE, the Web of Science and China National Knowledge Infrastructure websites. No ethical approval or written informed consent for participation was required.
: Not applicable.
: The authors declare that they have no competing interests.