Funding for this research was provided by:
Science and Technology Fund of Sichuan Province (2018JY0059)
Received: 10 May 2019
Accepted: 9 October 2019
First Online: 24 November 2019
Ethics approval and consent to participate
: This study is a data analysis of the literature and does not involve ethics or subject consent.
: Not applicable.
: The authors declare that they have no competing interests.