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Article History

Received: 30 October 2023

Accepted: 25 April 2025

First Online: 23 May 2025

Declarations

:

: There was no request for parental consent in 2010 and 2014. The survey in 2018 complied with the new Data Protection Act, under which data is collected (). It is legal to collect and process data from students at school where the processing takes place for the sole purpose of conducting statistical or scientific studies of significant importance to society. There was no request for obtaining written approval from individual parents or schoolchildren. Prior to the survey in 2018 we provided written information to the parents about the study, as requested in the new legislation.

: According to Sect. 14 in the Danish Scientific Ethical Committees Act, there is no request for ethics approval of population-based questionnaire surveys and there was no agency to provide approval in 2010, 2014 and 2018 (). In all surveys, we received approval from the school principal, the school board representing the parents, and the board of schoolchildren representing the schoolchildren in every participating school. We informed the participants orally and in writing about the purpose of the study, that data collection was anonymous and voluntary.

: The surveys in 2010 and 2014 were as requested registered at the Danish Data Protection Authority (J. No. 2013-54-0567) and the survey in 2018 as requested registered within the institution (Case 10 622, University of Southern Denmark). The research group had no access to information that can identify participants.

: The authors declare that they have no competing interests.