Funding for this research was provided by:
Vietnam Ministry of Education and Training (. B2020-SPH-11)
Article History
Received: 14 September 2019
Accepted: 28 May 2020
First Online: 16 June 2020
Ethics approval and consent to participate
: Not applicable. The study does not involve human subjects, only use public data.
: Not applicable.
: The authors declare that there is no competing interest in relation to the publication of this article.