Yu, Zihang
Xu, Lingzhong
Sun, Long
Zhang, Jiao
Qin, Wenzhe
Li, Jiajia
Ding, Gan
Wang, Qian
Zhu, Jing
Xie, Su
Funding for this research was provided by:
National Natural Science Foundation of China (71673169, 71673170)
Article History
Received: 24 October 2018
Accepted: 18 June 2019
First Online: 3 July 2019
Ethics approval and consent to participate
: The verbal informed consent was obtained from each participant prior to the survey and Academic Research Ethics Committee of Shandong University School of Public Health confirmed this form of consent and approved the study protocol.
: Not applicable.
: The authors declare that they have no competing interests.