Funding for this research was provided by:
Received: 24 May 2019
Accepted: 23 October 2019
First Online: 6 November 2019
Ethics approval and consent to participate
: The study was approved by The Regional Committee for Research Ethics in Norway (REK 08/206d, 2008/2900, 09/2413) and by the Privacy Issues Unit, Norwegian Social Science Data Services (NSD no. 18782). Written informed consent was obtained from all study participants.
: Not applicable.
: The authors declare that they have no competing interests.