Funding for this research was provided by:
National Natural Science Foundation of China (71804201)
Natural Science Foundation of Guangdong Province (2018A0303130046, 2017A030310346)
Sun Yat-Sen University Scientific Research Foundation (17ykpy15)
Received: 20 December 2019
Accepted: 15 September 2020
First Online: 21 September 2020
Ethics approval and consent to participate
: The analysis is based on CHARLS data open to researchers. The original CHARLS was a survey approved by the Ethics Review Committee of Peking University, and all participants gave written informed consent at the time of participation.
: Not applicable.
: The authors declare that they have no competing interests.