The adolescents reported on their alcohol use frequency in the past month using the following categorical response options: “never”, “less often than once a month”, “about 1–2 times a month” or “once a week or more”. We then transformed this categorical variable into a semi-continuous variable indexing the approximate number of days (out of 30) the adolescent drank in the past month. The answer choices were recoded as following: never = 0, “less often than once a month” = 0.5, “about 1–2 times a month” = 1.5, and “once a week or more” = 4.3. Therefore, 0, 0.5, 1.5 and 4.3 equal the approximate number of days in a month (30 days) that the adolescent drank corresponding to the ordinal response options (Dick et al., 2001).
