Funding for this research was provided by:
National Natural Science Foundation of China (81373882)
Text and Data Mining valid from 2019-08-12
Received: 31 January 2019
Accepted: 30 July 2019
First Online: 12 August 2019
Ethics approval and consent to participate
: This project was approved by the Research Ethics Committee of the first hospital of Lanzhou University, Lanzhou, China (LDYYL2013–0007). The informed consent was obtained of all the participants before the survey.
: Not applicable.
: All authors have completed the Unified Competing Interest form. KY reports a grant from the National Natural Science Foundation of China (NNSFC) during the conduct of the study. YC reports a grant from NNSFC for another project, which has no role for this study. There were no other relationships or activities that could appear to have influenced the submitted work.