Funding for this research was provided by:
National Natural Science Foundation of China (71704194)
Natural Science Foundation of Guangdong Province (2016A030313204)
Text and Data Mining valid from 2020-02-14
Received: 28 June 2019
Accepted: 5 February 2020
First Online: 14 February 2020
Ethics approval and consent to participate
: This study was approved by the Institutional Review Board of School of Public Health, Sun Yat-Sen University (No. 201533).
: Not applicable.
: The authors declare that they have no competing interests.