Funding for this research was provided by:
Norges Forskningsråd (213759/H10)
National Institute on Drug Abuse (R01-DA012140)
Australian Research Council (DPO663371, DPO877359, and DP1095744)
Australian National Health and Medical Research Council (NHMRC: 594793)
Received: 15 August 2018
Accepted: 3 June 2019
First Online: 21 June 2019
Ethics approval and consent to participate
: The Norwegian TOPP study has been approved by the Norwegian Data Protection Authority and the Regional Committees for Medical and Health Research Ethics (REC) South East Norway. The TOPP study started in 1992/1993 when written consent in research studies was not a requirement. However, in later years, REC has reviewed all information given to participants and concluded that the study fulfils essential requirements for informed consent. Study participation was voluntary. Information about the study, the possibility to skip questions, and the right to withdraw from the study at any point, was provided in writing to both the children and their mothers for each data collection. The children were invited through their mothers, who were given questionnaires and separate envelopes for themselves and their children. In the Australian IYDS study, ethics approval was first gained through the Ethics in Human Research Office at the Royal Children’s Hospital in Victoria. At time 1, permission was then gained from the Victorian Department of Education and Training for government schools and the Catholic Education Office for some private schools and then by school principals. Parents provided written consent for their child to participate in the study and students provided assent to complete the survey. At time 7, ethics approval was gained through The University of Melbourne Human Ethics in Research Committee and young adult participants provided online assent at the time of survey completion.
: Not applicable.
: The authors declare that they have no competing interests.