Participants reported whether they had ever drunk beer, wine, wine coolers, whiskey, gin, or other liquor (alcohol use); or used marijuana (Brody et al., 2009). These items were scored dichotomously as 1 for yes (ever used alcohol, or used marijuana) and 0 for no. The two items were summed to form a substance use initiation index that could range from 0 to 2 at each assessment. The mean substance use initiation index score was .13 (SD = .34) at pretest (age 11) and .34 (SD = .54) at wave 3 (age 13).
