Outcome Measures
We selected standard measures of substance use that are used in statewide surveys in Grades 6—12 (Washington State Department of Social and Health Services, Consistent with national and state surveys, response scales for each item were on a 7-point ordinal scale ranging from 0 occasions to 40 or more occasions. Because distributions were heavily skewed, we dichotomized each of these variables into “none in past 30 days” (or “over the past two weeks” for binge drinking) and “at least once in past 30 days/two weeks.” Beginning with cohort 2, we included the additional option of “I have never done this” and dichotomized responses to this item into a lifetime use variable (“never used” or “used”); this option was inadvertently omitted from the survey administered to cohort 1. thus, we have information on lifetime use of substances for cohort 2 but not for cohort 1.