Funding for this research was provided by:
Sykehuset Innlandet HF
Received: 24 May 2019
Accepted: 16 October 2019
First Online: 12 November 2019
Ethics approval and consent to participate
: Written consent by parents for students who were younger than 16 years and by students who were older than 16 years was obtained on both occasions. The Regional Committee for Medical Research Ethics; Region South East, (University of Oslo), approved the study in both 2002 and 2017 (2017 project number: 2016/1755).
: Not applicable.
: The authors declare that they have no competing interest.