born in that country from 1902 to 1949 (nearly 9,000 male pairs), and Swedish temperance board registrations from 1929 to 1974 (about 2,500 twins). Subjects came to the attention of temperance boards mostly because of alcoholism or crimes related to drinking. In this study, although the prevalence of temperance board registrations was similar in monozygotic (MZ) and dizygotic (DZ) twins, the concordance rate for such registration was significantly higher in MZ twins. Moreover, as in Heath et al. (1997) study, heritability was stable over time, suggesting that in this sample the environmental contributions to the risk for AD were also stable over time, and that major social and historical changes did not affect environmentally determined AD risk. Using tetrachoric correlation and model fitting, twin resemblance was attributed to genetic factors (54%), family environment factors (14%), and non-shared environmental factors (remainder). It is notable that such a complex and detailed analysis yielded results consistent with other studies of AD, and over time within the study—using essentially ad hoc diagnostic criteria (i.e., temperance board registration). Thus, the diagnostic constructs used for AD for which genetic liability can be estimated appear to be valid and meaningful in terms of the consequences and outcomes
