Funding for this research was provided by:
National Natural Science Foundation of China (81671324, 81371465)
National Key R&D Program of China (2017YFC1310400)
Research Foundation of Education Bureau of Hunan Province (17C0122)
Received: 30 September 2019
Accepted: 21 January 2020
First Online: 30 January 2020
Ethics approval and consent to participate
: Given that some of the participants aged under 18, we sent verbal informed consent to their parents (or legal guardians) with the help of the class advisers prior to the survey. We only obtained the verbal consent through message because the participants are almost residential students who meet their parents (or legal guardians) merely during the holidays. The study protocol emphasized the foregoing irresistible clause (i.e., only verbal consent could be obtained) and was approved by the Ethics Committee of the Second Xiangya Hospital of Central South University.
: Not applicable.
: The authors declare that they have no competing interests.