Based on responses to smoking history questions, individuals were categorized as current smokers, former smokers, or non-smokers. Former smokers were those who had smoked 100 or more cigarettes in their lives, but none in the past 12 months, while current smokers were defined as those who crossed the 100-cigarette threshold and had also smoked in the past 12 months. Non-smokers were those who never crossed the 100-cigarette threshold. The estimated number of drinks per month during the previous 12 months, was computed from retrospective self-report by multiplying the typical frequency of drinking a given beverage by the number of drinks of that beverage consumed on a typical occasion. This value was included as a continuous variable in several analyses. Subjects were also categorized by their DSM-IV alcohol dependence status, with “Current” alcohol dependent subjects meeting criteria for a past-year diagnosis, and “Former” alcohol dependent subjects meeting criteria for alcohol dependence prior to, but not during, the past 12 months. The same approach was taken for drug dependence, with all separate types of drug dependence assessed in both NLAES and NESARC
