Funding for this research was provided by:
National Natural Science Foundation of China (81530087)
Received: 6 November 2019
Accepted: 16 September 2020
First Online: 25 September 2020
Ethics approval and consent to participate
: Each participant included in this study signed a written informed consent form before taking the survey. Ethics approval for the data collection in CHARLS was obtained from the Biomedical Ethics Review Committee of Peking University (IRB00001052-11015).
: All authors approved the final manuscript for submission and gave consent for publication.
: The authors declare that they have no competing interests.