Article History
Received: 12 November 2018
Accepted: 13 February 2019
First Online: 22 February 2019
Compliance with ethical standards
:
: The authors declare that they have no conflict of interest.
: All procedures performed in this study involving human participants were in accordance with the ethical standards of the research committee of Hunan University and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards.
: Written informed consent was obtained from all the surveyed participants.