The assessment protocol was based on the semi-structured assessment of the genetics of alcoholism (Australian version; SSAGA-OZ) and administered using a computer-administered telephone interview (Bucholz et al., 1994; Heath et al., 1997) used in a previous ‘1989’ cohort of Australian twins born between 1964 and 1971 (Knopik et al., 2004). This instrument obtains full diagnostic criteria for cannabis and other illicit drug abuse and dependence. In addition, we assessed specific aspects of experience with cannabis and other illicit drugs, including exposure opportunity, initial subjective reactions to cannabis and components of cannabis withdrawal, and full DSM-IV diagnostic criteria for a number of other diagnoses (MDD, childhood conduct disorder, alcohol and nicotine dependence, panic disorder). The SSAGA, from which this interview assessment was derived, has been shown to have good reliability and validity as a measure of standardized DSM-IV diagnostic criteria for a range of conditions including alcohol abuse and dependence, nicotine dependence, MDD, and antisocial personality disorder (Bucholz et al., 1994).
