Funding for this research was provided by:
the National Social Science Fund of China (18BGL218)
Text and Data Mining valid from 2019-07-29
Received: 13 May 2019
Accepted: 22 July 2019
First Online: 29 July 2019
Ethics approval and consent to participate
: The CHARLS was approved by the Ethics Committee of Peking University Health Science Center. All participants gave written informed consent before recruited into the study.
: Not applicable.
: The authors declare that they have no competing interests.