Funding for this research was provided by:
Canada Excellence Research Chairs, Government of Canada
Received: 20 October 2020
Accepted: 30 April 2021
First Online: 22 May 2021
: Ethics approval for the 1970–1996 cycles was granted from a UK National Health Service ethics review board. Starting in the 2000 cycle, ethics approval was acquired from multicentre research ethics committees [CitationRef removed]. Ethics for the secondary analysis presented in this paper was obtained from the General Research Ethics Board at Queen’s University. In the 1970 cycle, consent was obtained by parents verbally agreeing to participate in the interview or by returning the questionnaire. In the 1975–1986 cycles, informed parental consent was obtained. In the 1996–2016 cycles, participants gave written consent.
: Not applicable.
: The authors declare that they have no competing interests.