The participants comprised an older and younger cohort of twins (detailed in the Supplementary Information Table I supp.) from the Australian NHMRC Twin Register and are of predominantly (97%) Northern European ancestry. All provided written informed consent under study protocols approved by the Queensland Institute of Medical Research Human Research Ethics Committee. During the period 1988–1990 study participants were mailed an extensive Health and Lifestyle Questionnaire (HLQ) containing items addressing SLEs and depression (N = 16,154, response rate 82%). The symptoms of anxiety and depression in the older cohort are typical of the Australian population [Kendler et al., 1986], although the level of education completed is higher, particularly for males [Baker et al., 1996]. Over the period 1992–2000, participants were interviewed by telephone using a version of the SSAGA (Semi-Structured Assessment for the Genetics of Alcoholism) modified for use in Australia (N = 16,302 response rate 83%), a comprehensive psychiatric interview assessing the physical, psychological, and social manifestations of alcoholism and psychiatric disorders in adults [Bucholz et al., 1994, 1995; Hesselbrock et al., 1999] according to DSM-IV criteria [American-Psychiatric-Association, 1987].
