Funding for this research was provided by:
National Social Science Fund of China (17BRK028)
Received: 26 October 2020
Accepted: 7 March 2021
First Online: 19 March 2021
: The study was approved by Institutional Ethical Committee of South China University of Technology. Preparation of this manuscript was performed in accordance with the ethical standards laid down in the 1964 Declaration of Helsinki and its later amendments. The manuscript does not contain clinical studies or patient data. All data were drawn from tabulations published by the authority of National Statistical Bureau of the People’s Republic of China, without any individual details, images, or videos. The Chinese census takers obtained informed consent from participants when sampling.
: Consent for publication was obtained from each participant during the informed consent process.
: That authors declare that they have no competing interests.