Four items were used to assess substance use (Johnston, O’Malley, & Bachman, 2000). At pretest and 22-month follow-up, youths reported on a scale ranging from 0 (not at all) to 6 (about two packs a day) how often during the past month they had smoked cigarettes. Youths also reported on a scale ranging from 0 (none) to 6 (30 or more times) how often during the past 3 months they (a) had a drink of alcohol, (b) had three or more drinks of alcohol at one time, or (c) had used marijuana. Responses to the four items were summed to form the substance use index.
