Funding for this research was provided by:
National Natural Science Foundation of China (41571527)
Sichuan Center for Rural Development Research Project (01781912)
Text and Data Mining valid from 2020-01-02
Received: 11 June 2019
Accepted: 16 December 2019
First Online: 2 January 2020
Ethics approval and consent to participate
: All procedures performed in 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. All participants in this study were provided with explanations via face-to-face interpretation as to the purpose and method of the investigation as well as possible risks and benefits of the study. Written informed consent was given prior to the investigation and the research did not contain medical records.
: Not Applicable.
: The authors declare that they have no competing interests.