Funding for this research was provided by:
National Natural Science Foundation of China (81573207)
Key Technologies Research and Development Program (2018YFC2000400)
Construction of High-level University in Guangdong of China (G618339167, C1051007)
the University Revitalization Program in Eastern, Western and Northern Guangdong (G619080438)
Text and Data Mining valid from 2019-11-05
Received: 29 May 2019
Accepted: 16 October 2019
First Online: 5 November 2019
Ethics approval and consent to participate
: This study uses a public use dataset and therefore does not require additional Institutional Review Board approval. Primary data collection for the Health and Retirement Study was approved by the Institutional Review Board at the University of Michigan.
: Not applicable.
: The authors declare that they have no competing interests.