The prevalence of alcohol use and dependence in the sample being studied is shown in table 1 in a form relevant to DTSA. In DTSA, for each outcome, those who have the possibility of suffering the outcome in each age range are the at-risk group. The at-risk group in the youngest age range is the entire sample. In each succeeding age range those who have suffered the outcome previously or for whom no information for that age range is available are removed from the at-risk group. Consequently the at-risk group diminishes in size in each successive age range. Because more subjects become regular users of alcohol than become alcohol dependent in each age range, the at-risk group for alcohol dependence is increasingly larger than the at-risk group for regular alcohol use in each subsequent age range. The illicit drug use subsample is also characterized in the table.
