Each DTSA model had the following structure: The outcomes, or dependent variables were either alcohol dependence or regular alcohol use. Regular alcohol use was defined as consumption at least once a month for 6 or more consecutive months. In all cases four distinct age ranges were used: under 16, 16 and 17, 18 and 19, over 19. These age groups were determined by the fact that ages of onset were whole numbers of years, that the numbers of those who became alcohol dependent be about the same in each group, and that there be at least 50 subjects in each group who became alcohol dependent to provide a reasonable degree of statistical reliability in the calculations. The same age grouping was used for regular alcohol use for comparative purposes. The covariates (predictive variables) were a genotype from a CHRM2 SNP, ERO power (delta 1–3 Hz) from one of the leads, family type (multiplex alcohol family or community family), number of parents who smoke, gender, and scores on principal components 1 and 2 derived from the stratification analysis of the sample
