Article History
Received: 19 March 2020
Accepted: 18 June 2020
First Online: 27 June 2020
Ethics approval and consent to participate
: The study was approved by the Regional Committee for Medical and Health Research Ethics, Southern Norway (REC ID: 2012/1155 approved 01/02/2013). All participants provided written informed consent. The study followed the Declaration of Helsinki.
: Not applicable.
: Ivar N. Omenås declares no conflict of interest.Christian Tronstad declares no conflict of interest.Leiv Arne Rosseland declares no conflict of interest.