The Substance Abuse Module (SAM) of the Composite International Diagnostic Inventory (Robins et al., 1988), modified to include questions about drinking frequency and quantity, was used to diagnose nicotine dependence, alcohol abuse or dependence, and illicit drug abuse or dependence. The adolescent's primary caretaker, typically the mother, was also interviewed about each twin using the parent version of the DICA–R. Mothers were interviewed as well about their own mental health; maternal lifetime alcohol dependence was assessed using the SAM.
