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Article History

Received: 19 February 2018

Accepted: 22 June 2018

First Online: 11 July 2018

Ethics approval and consent to participate

: The Danish Data Protection Agency granted permission for the study. All potential participants received written information about the study (the information letter) underscoring study objectives, anonymity procedures, participants’ rights to withdraw and that (non-)participation had no consequences for the individual. The intervention groups received further oral information from their teachers about the study where it was possible to ask questions. A person-encrypted database comprising both questionnaire and registry data to be used for the analyses was created by Statistics Denmark. According to Danish law, no approval from an ethics committee is required when human tissue is not part of the research project.

: Not applicable.

: The authors declare that they have no competing interests.

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