Funding for this research was provided by:
National Bureau of Statistics of China (2019LZ03)
Article History
Received: 31 January 2020
Accepted: 26 May 2020
First Online: 11 June 2020
Compliance with ethical standards
:
: This manuscript is an original work that has not been submitted to nor published anywhere else. All authors have read and approved the paper and have met the criteria for authorship listed above. All authors declare that they have no known competing financial interests or personal relationships.