Received: 3 September 2019
Accepted: 13 November 2019
First Online: 5 December 2019
Ethics approval and consent to participate
: This is a secondary data analysis which received no funding. All studies received institutional ethics approval, and informed consent was obtained from all individual participants (and/or parents where appropriate) included in the studies.
: Not applicable.
: The authors, Alex Rowlands, Nathan Dawkins, Ben Maylor, Charlotte Edwardson, Stuart Fairclough, Melanie Davies, Deirdre Harrington, Kamlesh Khunti, and Tom Yates, declare that they have no competing interests.