Funding for this research was provided by:
Helse Nord RHF (ID6877/SFP1053-12)
Received: 17 July 2017
Accepted: 10 January 2018
First Online: 19 January 2018
Ethical approval and consent to participate
: The Norwegian Data Protection Authority (reference number 2009/1282) and The Regional Committee of Medical and Health Research Ethics (2011/1702/REK Nord) approved the study in July 2010 and October 2011, respectively. Participants signed a declaration when arriving at the study site, in addition participants younger than 16 had to bring written permission from their guardians.
: Not applicable.
: All authors declare that they have no competing interests.
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