Funding for this research was provided by:
National Natural Science Foundation of China (81722039, 81673195)
Article History
Received: 11 January 2021
Revised: 17 August 2021
Accepted: 26 August 2021
First Online: 3 September 2021
Competing interests
: The authors declare no competing interests.
: The study protocol was approved by the Institutional Ethics Review Board of the School of Public Health, Shandong University.