Funding for this research was provided by:
Universitetet i Bergen
Universitetet i Oslo
Text and Data Mining valid from 2018-05-09
Received: 5 October 2017
Accepted: 30 April 2018
First Online: 9 May 2018
: 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.