Funding for this research was provided by:
National Natural Science Foundation of China (No.81673041)
Natural Science Foundation of Guangdong Province (No.2017A030313760)
Article History
Received: 5 August 2019
Accepted: 30 October 2019
First Online: 17 December 2019
Compliance with Ethical Standards
: All procedures performed within the study were in agreement with the ethical principles set by 1964 Declaration of Helsinki and its later amendments (2013). The protocol of the study was approved by the institutional ethics committee (Southern Medical University). All examinees have signed an informed consent form prior the inclusion into the study.
: The authors declare that they have no conflict of interest.