Funding for this research was provided by:
Received: 25 September 2019
Accepted: 4 February 2020
First Online: 17 February 2020
Ethics approval and consent to participate
: Ethics approval was not necessary under Danish law as this study did not include human biological material. Data collection and all local confidentiality and privacy requirements were met was approved by the Danish Data Protection Agency J. No. 2013-54-0526. The Danish Data Protection Agency also approved that participants under the age of 16 gave consent. Schools was encouraged to inform parents of the study. At the beginning of the questionnaire, participants had to read and accept an informed consent form that clearly expressed that participation was voluntary and that individual data would be kept confidential.
: Not Applicable.
: The authors declare that they have no competing interests.