Funding for this research was provided by:
National Natural Science Foundation of China (81673146)
Text and Data Mining valid from 2019-09-18
Received: 12 June 2019
Accepted: 9 September 2019
First Online: 18 September 2019
Ethics approval and consent to participate
: The study protocol and instruments were reviewed and approved by the Peking University Institutional Review Committee. Ethical approval identification code is IRB00001052–16071. The study was conducted according to the guidelines of the Declaration of Helsinki. Prior to the study, all participants read and signed the informed consent form.
: Not applicable.
: The authors declare that they have no competing interests.