Text and Data Mining valid from 2018-04-24
Received: 17 August 2017
Accepted: 22 March 2018
First Online: 24 April 2018
Ethics approval and consent to participate
: This research only used publicly-available, secondary data sources and thus did not require ethics approval or consent to participate.
: Not applicable.
: The authors declare that they have no competing interests.
: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.