Funding for this research was provided by:
Natural Science Foundation of Beijing Municipality (7172250)
National Natural Science Foundation of China (81261120566, 81970714)
Received: 17 May 2019
Accepted: 28 October 2019
First Online: 9 November 2019
Ethics approval and consent to participate
: The study has been approved by the ethics committee at Pinggu Campus of Capital University Beijing Friendship Hospital. All participants provided written informed consent for their participation in the survey.
: Not applicable.
: The authors declare that they have no competing interests.