Text and Data Mining valid from 2019-02-28
Received: 1 October 2018
Accepted: 19 February 2019
First Online: 28 February 2019
Ethics approval and consent to participate
: The need for ethics approval by an institutional board review was waived as this study does not directly involve human subjects.
: Not applicable because this study does not directly involve human subjects.
: The authors declare that they have no competing interest.
: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.