Received: 5 May 2020
Accepted: 21 November 2020
First Online: 6 January 2021
Ethics approval and consent to participate
: The study protocol was approved by the Institutional Review Board of Peking University, Beijing, China. All participants gave written consent after being informed to the aim of the survey and their rights to refuse to participate.
: Not applicable.
: The authors declare that they have no competing interests.