Text and Data Mining valid from 2018-03-27
Received: 20 November 2017
Accepted: 5 March 2018
First Online: 27 March 2018
Ethics approval and consent to participate
: This study did not require the approval of an ethics committee as it is a secondary analysis of a database of a public domain and of free access.
: This study did not require consent for publication.
: The authors declare that they have no competing interests.
: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.