Funding for this research was provided by:
National Natural Science Foundation of China (71473152, 71774104, 71003067)
China Medical Board (16-257)
Cheeloo Youth Scholar Grant, and Shandong University (2009TS012, 2012DX006)
Text and Data Mining valid from 2019-09-02
Received: 2 October 2018
Accepted: 22 August 2019
First Online: 2 September 2019
Ethics approval and consent to participate
: This study was approved by Ethical Committee of Shandong University School of Public Health. Before the interview, the purpose of the study was explained to the participants and written informed consents were obtained from each of the participants.
: Not applicable.
: The authors declare that they have no competing interests.