Funding for this research was provided by:
National Natural Science Foundation of China (81571341)
National Basic Research Program of China (973 Program) (2016YFC800701)
Received: 20 May 2019
Accepted: 25 August 2019
First Online: 2 September 2019
Ethics approval and consent to participate
: This study was approved by the Human Ethics Committee of the Second Xiangya Hospital of Central South University<b>.</b> All participants were informed of the objective of the study and gave written consent before the investigation.
: Not applicable
: Runsen Chen is an associate editor of BMC Health Services Research. All other authors are no conflict of interest exists in carrying out this study and preparing the manuscript.