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Methods and results

The Dunedin multidisciplinary health and development study (a study of a general population birth cohort of 1037 individuals born in Dunedin, New Zealand, in 1972-3) 4 has a 96% follow up rate at age 26. It obtained information on psychotic symptoms at age 11 and drug use at ages 15 and 18 from self reports and assessed psychiatric symptoms at age 26 with a standardised interview schedule to obtain DSM-IV (diagnostic and statistical manual of mental disorders, 4th edition) diagnoses. We analysed data from a representative group of 759 (74%) living study members who had complete data on adult psychiatric outcomes, adolescent use of illicit substances, and childhood psychotic symptoms.