In young adulthood, the translated, adult version of the SSAGA, a comprehensive, semi-structured interview to assess substance dependence and related psychiatric disorders was administered [25]. The first questions of the substance use sections were developed to assess lifetime use and frequency of use of tobacco, alcohol and cannabis. For this study, frequency of tobacco use was defined as the number of events per day, including cigarettes, cigars, pipes and snus (Swedish type of smokeless tobacco). Four categories of daily tobacco use were distinguished, ranging from no daily tobacco use to 11 or more cigarettes, cigars, pipes or snus portions a day. Alcohol use was defined as the typical number of drinks a week, including beer, wine, spirits, and other alcoholic drinks. Five categories of alcohol use were distinguished, ranging from no/low levels of alcohol use (<3 alcoholic drinks a week) to high levels of use (15 or more drinks a week). Cannabis use was categorized as no lifetime use of cannabis, 1–2 times used during lifetime, and lifetime cannabis use of 3 times or more. For each substance, the number of categories was based on the distribution of the frequency of use. Table 1 presents the categories for each substance.
