Funding for this research was provided by:
The Norwegian Directorate of Health
Text and Data Mining valid from 2019-04-25
Received: 26 May 2018
Accepted: 2 April 2019
First Online: 25 April 2019
Ethics approval and consent to participate
: The Norwegian Western Regional Ethical Committee (REK) approved the study and the use of informed passive consent under the condition that a detailed information letter was given both in paper form and electronically to parents or custodians for all participants below the age of 16. Those that did not want their child to participate had to sign and return a form to the teacher. Approval of the child’s participation was assumed if the form was not returned.
: Not applicable.
: The authors declare that they have no competing interests.
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