Funding for this research was provided by:
Fundamental Research Funds for the Central Universities (2012017yjsy200)
Text and Data Mining valid from 2018-06-02
Received: 13 March 2018
Accepted: 23 May 2018
First Online: 2 June 2018
Compliance with ethical standards
: The authors declare that they have no conflict of interest.
: For this type of study, formal consent is not required.
: Informed consent was obtained from the parents or legal guardians of all individual participants included in the study.