Funding for this research was provided by:
National Natural Science Foundation of China (71704194)
Medical Science and Technology Foundation of Guangdong Province (2016A030313204)
Text and Data Mining valid from 2019-09-18
Received: 7 September 2018
Accepted: 11 September 2019
First Online: 18 September 2019
Ethics approval and consent to participate
: This study was approved by the Institutional Review Board of the School of Public Health, Sun Yat-sen University (Approval No. 2017012). As this study was retrospective in design, there is no need for consent to participate to be obtained. Administrative permissions from Guangzhou Social Insurance Bureau were required to access the raw data.
: No applicable.
: The authors declare that they have no competing interests.