Experimentation was defined for all substances as having used a substance one or more times in a person’s lifetime. Repeated alcohol use was defined as having had six or more drinks in a respondent’s lifetime. Repeated tobacco (cigarette) use was defined as ‘recently smoking regularly’ or ‘smoking regularly in the past’, allowing each respondent to define “regular smoking” themselves. Repeated marijuana use was defined as having used marijuana (grass, pot, or hashish) six or more times in a respondent’s lifetime. Abuse and dependence categories adhered to the 1+ and 3+ symptom endorsement guidelines (for abuse and dependence, respectively) of the Diagnostic and Statistical Manual of Mental Disorders 4th Ed. (DSM-IV; American Psychiatric Association (APA), 1994) but without imposing the clustering criterion or distinguishing between dependence with or without physiological symptoms. At Wave 1, clustering would have slightly reduced the prevalence of SUD diagnoses for alcohol (6-5.88%), marijuana (3.81-3.70%), and tobacco dependence (3.46-2.37%); based on this observation we chose not to impose clustering. Unlike the experimentation and repeated-use categories, DSM-IV abuse and dependence are mutually exclusive diagnoses, such that a diagnosis
