The excellent reliability and substantial heritability of our quantitative consumption factor score and its high genetic correlation with AD suggest that the factor score will be useful in the identification of genes contributing to AD. While it is possible that binary diagnostic AD measures may play a role in the discovery of genes contributing to heaviness of consumption, continuous measures such as consumption are considerably more powerful predictors than binary ones, and are therefore likely to be especially useful for detecting the numerous small effects that contribute to AD risk. Prior studies using diagnostic assessments of AD have been limited by loss of power (e.g., through use of affecteds-only) or by heterogeneity among the unaffected individuals. Use of a quantitative measure circumvents these challenges by allowing for assessment of genomic effects across the range of liability to dependence. The factor score also represents an improvement over AD symptom count measures, which are highly skewed. Our study also suggests that quantitative indices of alcohol consumption may allow investigators to indirectly examine genetic and genomic effects on AD vulnerability even in the
