Funding for this research was provided by:
National Natural Science Foundation of China (71901184)
Humanities and Social Science Fund of Ministry of Education of China (19YJCZH119)
National Statistical Scientific Research Project (2018LY42)
Article History
Received: 2 June 2019
Revised: 7 August 2020
Accepted: 21 August 2020
First Online: 4 September 2020
Free to read: This content has been made available to all.