Funding for this research was provided by:
Yanta Scholars Foundation of Xi’an University of Finance and Economics
National Natural Science Foundation of China (11601404)
National Statistical Research Program (2016LZ37)
Talent development foundation of Xian University of Finance and Economics
Youth Innovation Teamiessit of Shaanxi Univer
Article History
First Online: 20 June 2019
Compliance with ethical standards
:
: Author Wei Gao declares that she has no conflict of interest. Author Haizhong Yang declares that he has no conflict of interest. Author Lu Yang declares that she has no conflict of interest.
: This article does not contain any studies with human or animal participants performed by the author.
: Informed consent was obtained from all individual participants included in the study.