Funding for this research was provided by:
National Natural Science Foundation of China (71774104)
Text and Data Mining valid from 2020-04-22
Received: 6 September 2019
Accepted: 6 April 2020
First Online: 22 April 2020
Ethics approval and consent to participate
: The study protocol was approved by The Ethical Committee of Shandong University School of Public Health. The investigation was performed after the acquisition of written informed consents of all participants.
: Not applicable.
: The authors declare there are no competing interests.