Received: 30 May 2018
Accepted: 1 May 2019
First Online: 10 May 2019
Ethics approval and consent to participate
: The study was approved by the Danish Data Protection Agency (no. 1–16–02-461-16). No consent was obtained from a parent or guardian on behalf of any participants. It was voluntary for the adolescents to answer the questionnaire, and they had the right to withdraw their undertaking of participation at any time. All the answers were treated strictly confidential, and the adolescents were guaranteed full anonymity. All procedures followed were in accordance with the ethical standards of the Helsinki Declaration of 1975, as revised in 2000.
: Not applicable.
: The authors declare that they have no competing interests.
: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.