This paper is supported by the Humanities and Social Sciences Foundation for the Youth Scholars of Ministry of Education of China (15YJCZH066), the Science and Technology Plan Project of Hunan Province (2016TP1020), the Science and Technology Plan Project of Hengyang City (2017KJ183), Hunan Provincial Natural Science Foundation of China (2018JJ4024), the Scientific Research Fund of Hunan Provincial Education Department (17A030), and the 2018 National Statistical Science Research Project of China (2018LY05).