- Correspondence to Hai Fang, China Center for Health Development Studies, Peking University, Beijing 100083, China;
- Received January 13, 2020
- Revised April 28, 2020
- Accepted July 31, 2020
- First published August 28, 2020.
If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.