Funding for this research was provided by:
Natural Science Fund of Hunan Province (#06JJ4045)
Education Innovation Project of Central South University (#2340-77324)
Text and Data Mining valid from 2017-09-02
Received: 24 January 2017
Accepted: 27 July 2017
First Online: 2 September 2017
Ethics approval and consent to participate
: Ethical committees from Central South University, the Health Department of Hunan provinces and all five counties have approved the research protocol. Before the data collection, permission of principals and teachers were got from 15 schools and received all informed consent forms from the students included in our research.
: Consent for personal data publication was obtained from the participants and their parents or their grandparents.
: The authors declare that they have no competing interests.
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