Received: 9 March 2019
Accepted: 25 July 2019
First Online: 16 August 2019
Ethics approval and consent to participate
: The research was performed in accordance with the Declaration of Helsinki and approved by the Regional Committee on Medical Ethics in Norway (REC S-08288a-2008/8618). The participants signed an informed consent form prior to participation in the study.
: Not applicable.
: The authors declare that they have no competing interests.