Funding for this research was provided by:
National Natural Science Foundation of China (71704006)
Beijing Social Science Fund (16SRB006)
Article History
Received: 26 December 2020
Accepted: 27 February 2021
First Online: 20 March 2021
Declarations
:
: The authors declare no conflict of interest.
: The protocols of CHARLS were approved by the Ethical Committee at Peking University. All participants in CHARLS gave informed consent.