For Cohort I, lifetime history of AD and AB were coded from DSM-IV symptoms based on a DSM-III-R assessment. The SSAGA administered to Cohort I predates DSM-IV; however, we applied an approximate algorithm for DSM-IV criteria without clustering that was developed by Heath and colleagues (see Heath, Whitfield, Madden, Bucholz, Dinwiddie et al., 2001). Consistent with other reports (Grant, Heath, Bucholz, Madden, Agrawal et al., 2007; Knopik et al., 2006; Waldron, Heath, Bucholz, Madden, & Martin, 2008), twins in Cohort I were diagnosed with AD if they endorsed three or more DSM-IV AD symptoms. Female twins were diagnosed with AB if they reported at least one symptom of DSM-IV AB. For Cohort II, DSM-IV AD was directly assessed, as was DSM-IV AB for female twins.
