Funding for this research was provided by:
Shaanxi Provincial Health Research Fund (No 2016E013)
Received: 11 February 2020
Accepted: 11 August 2020
First Online: 23 September 2020
Ethics approval and consent to participate
: The original CHARLS was approved by the Ethical Review Committee of Peking University, and all participants signed informed consent at the time of participation. The study methodology was carried out in accordance with approved guidelines.
: Not applicable.
: The authors declare that they have no competing interests.