The sample comprised participants from the Avon Longitudinal Study of Parents and Children (ALSPAC) 14,15. Pregnant women resident in the former Avon Health Authority (Bristol) in South West England with an estimated date of delivery between 1 April 1991 and 31 December 1992 were invited to take part, resulting in a ‘core’ cohort of 14 541 pregnancies and 13 617 singletons alive at 12 months of age. Within this sample, 7218 singleton individuals had information allowing the derivation of conduct problem trajectory. Of these individuals, 4159 (57.6%) had information on cannabis use at age 16, 2393 of these individuals were girls (4822 individuals in total provided information on cannabis use at 16). The primary source of data collection was via self-completion questionnaires administered at least annually to the mother, her partner and the ALSPAC study child. Since the age of 7 years the whole offspring cohort has been invited to annual ‘focus’ clinic for a variety of hands-on assessments. More detailed information on the ALSPAC study is available at http://www.alspac.bris.ac.uk. All aspects of the study were reviewed and approved by
