Funding for this research was provided by:
Norges Forskningsråd (226524)
Received: 17 January 2017
Accepted: 10 January 2018
First Online: 15 January 2018
Ethics approval and consent to participate
: The study was approved by the Norwegian Centre for Research Data - NSD (reference no. 37655). All participants signed a written form of consent after having received oral and written information about the study.
: Not applicable.
: Authors declare that they have no competing interests.
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