Two longitudinal measures of over-time alcohol consumption were used as phenotypic outcomes. Both measures were derived from repeated assessments of average drinks per week. The first measure, as detailed below, was a developmental trajectory estimate of alcohol consumption (drinks per week) across adolescence and early adulthood (maximum age range: 8–30). Intuitively, this trajectory slope measures the rate at which alcohol consumption increases, starting with no consumption for virtually all subjects in childhood, then increasing at different rates (or remaining flat among non-drinkers) through adolescence and the transition to adulthood, before stabilizing at different levels in the late twenties. The second measure was the simple mean of all alcohol consumption (drinks per week) repeated assessments collected across adolescence and the transition to adulthood (maximum age range: 12–21) for each subject. We selected these two specifications as: (1) the trajectory outcome was derived from the best fitting longitudinal model of the several tested, and maximized power through including all repeated measures, while (2) the mean consumption outcome provided a simpler summary of individuals’ drinking behavior, and thus greater continuity to existing literature
