国家自然科学基金71201147;教育部人文社会科学研究项目12YJC630161;全国统计科学研究项目2014511;国家留学基金201506335018National Natural Science Foundation of China71201147;Humanities and Social Science Project of Ministry of Education12YJC630161;National Statistical Science Research Project of China2014511;China Scholarship Council201506335018