Participants were recruited from 1992 to 1995 for a telephone interview based twin study conducted at the Queensland Institute of Medical Research (QIMR; Heath et al., 1997). This interview was based upon an Australian modified version (SSAGA-OZ) of the Semi-Structured Assessment for the Genetics of Alcoholism instrument (SSAGA; Bucholz et al., 1994) designed for genetic studies of alcoholism. The SSAGA is a psychiatric interview which retrospectively assesses physical, psychological and social manifestations of AD along with several other psychiatric disorders (American Psychiatric Association, 1994) and has undergone both reliability and validity testing (Bucholz et al., 1994; Hesselbrock et al., 1999). A total of 4597 subjects (34.6% males) from 2618 families comprising 814 (583 female and 231 male) monozygotic (MZ) pairs, 1177 (482 female, 198 male and 491 opposite sex) dizygotic (DZ) pairs and 627 twins (38.8% male) whose co-twin did not particpate were included in genetic analysis. The participants were predominantly of Northern European ancestry (>90%) and aged 26 to 89 years (mean age was 43.8 ± 11.5 years) at the time of testing. Subjects gave written informed consent and
