All participants completed semi-structured diagnostic interviews. Interviews for case and neighborhood control participants were completed in person; interviews for twin sample controls were completed via telephone. Substance dependence diagnostic sections of the interview were based on the Semi-Structured Assessment for the Genetics of Alcoholism - Australia (SSAGA-OZ) (Bucholz et al. 1994) enabling DSM-IV and DSM-III-R lifetime diagnoses of opioid, cannabis, sedative, stimulant, cocaine, and alcohol abuse and dependence. The nicotine dependence section of the interview was modified from the Nicotine Addiction Genetics Study (Hansell et al. 2009) assessment which was derived from the World Health Organization Composite International Diagnostic Interview (CIDI) (Andrews & Peters 1998). Similar diagnoses were obtained for CATS pilot project participants (25 cases and 25 neighborhood controls) via the CIDI (Andrews & Peters 1998).
