Article History
Received: 11 September 2018
Accepted: 30 January 2019
First Online: 8 March 2019
Compliance with ethical standards
:
: On behalf of all authors, the corresponding author states that there is no conflict of interest.
: The British Child and Adolescent Mental Health Surveys and Millennium Cohort Study received ethical approval from the Multi-Centre Research Ethics Committee. Parents in all three studies provided informed consent.