Article History
Received: 5 June 2020
Accepted: 9 September 2020
First Online: 17 September 2020
Ethics approval and consent to participate
: Ethical approval was obtained from the Institutional Review Board for Human Subject Research, Research Center for Public Health at Tsinghua University (Beijing, China; Reference No. THUSM/PHREC/2020400–001).
: Not applicable.
: Not applicable.