Funding for this research was provided by:
National Natural Science Foundation of China (71373183, 71603188)
Fundamental Research Funds for the Central Universities (2018QN051)
Social Science Youth Foundation from the Ministry of Education of China (16YJCZH137)
Text and Data Mining valid from 2019-03-11
Received: 24 September 2018
Accepted: 21 February 2019
First Online: 11 March 2019
Ethics approval and consent to participate
: The NHSS obtained ethics approval (license number: 2008 (18) and 2013 (65)) from the institutional review board of the Chinese National Bureau of Statistics. All procedures performed in the studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. The interviewers explained the purpose of the survey before obtaining oral informed consent from the individual participants.
: Not applicable.
: The authors declare that they have no competing interests.
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