Funding for this research was provided by:
National Natural Science Foundation of China (71403008)
Text and Data Mining valid from 2019-09-02
Received: 14 January 2019
Accepted: 1 August 2019
First Online: 2 September 2019
Ethics approval and consent to participate
: The study has been approved by the Ethics Review Board of the School of Public Health, Peking University. Informed consent was obtained from all participants prior to questionnaire administration.
: Not applicable.
: The authors declare that they have no competing interests.