[1] Univ Oxford, Warneford Hosp, Dept Psychiat, Oxford OX3 7JX, England
[2] LSHTM, Ctr Stat Methodol, London WC1E 7HT, England
[3] Karolinska Inst, Dept Publ Hlth Sci, S-17177 Stockholm, Sweden
[4] UCL, Inst Child Hlth, London WC1N 1EH, England
[5] Univ Bristol, Sch Social & Community Med, Bristol BS8 2BN, Avon, England
[6] UCL, Fac Brain Sci, Mental Hlth Sci Unit, London W1W 7EJ, England