Control genotype data were available for 1156 individuals (594 men, 562 women) born in the UK during one week in 1958 (the 1958 British Birth Cohort). All available data were included. The sample was genotyped by the Wellcome Trust Case-Control Consortium,19 from whom we obtained permission to use the data. Psychiatric data were not available for the control cohort. For disorders of low frequency (1–2% prevalence of ADHD), the effect of unscreened controls would be negligible. Over-representation of affected individuals in the control sample would only reduce power to detect association.
