Høgholen, H
Storhaug, A
Kvernrød, K
Kostovski, E
Viktil, K K
Mathiesen, L
Article History
Received: 4 May 2017
Revised: 10 July 2017
Accepted: 11 July 2017
First Online: 29 August 2017
Competing interests
: The authors declare no conflict of interest.