Funding for this research was provided by:
National Natural Science Foundation of China (71573097, 71233001)
National Basic Research Program of China (2013CB530700)
Received: 25 September 2019
Accepted: 19 March 2020
First Online: 6 April 2020
Ethics approval and consent to participate
: The CLHLS study was approved by the Research Ethics Committee of Peking University (IRB00001052–13074), and all participants or their proxy respondents provided written informed consent.
: Not applicable.
: The authors declare that they have no competing interests.