Maternal postnatal cannabis use (‘yes’ indicating a positive response at either 2, 8, 21 or 33 months postnatal), maternal daily alcohol use (‘yes’ indicating a positive response at either 2, 8, 21 or 33 months postnatal), maternal smoking (none/one to 19 cigarettes per day/20+ per day, indicating the greatest amount reported at either 2, 8, 21 or 33 months postnatal), maternal postnatal depressive symptoms [achieving a score of 13 or higher on the Edinburgh Postnatal Depression Scale (EPDS) 19 at either 2, 8, 21 or 33 months postnatal] and antenatal maternal depressive symptoms (achieving a score of 13 or higher on the EPDS at either 18 or 32 weeks gestation). Additional data were also available on the substance use behaviour of the mother's partner. These data were used in preliminary analyses but were not taken forward to the final multivariable models due to poorer response rates, strong collinearity with the maternal measures, similarity in associations (compared with the maternal measures) and issues with imputing this information when the young person has only one parent.
