Regular smoking was assessed through two questions. Respondents were asked, “Have you ever smoked cigarettes regularly—that is, at least a few cigarettes every day?” Those responding “yes” were then asked, “On average, about how many cigarettes did you smoke per day during the one year in your life when you smoked most heavily?” Respondents indicating that they smoked less than three cigarettes per day during the time of heaviest smoking were considered to have never been regular smokers. Respondents indicating that they had smoked regularly were also asked, “At what age did you begin smoking regularly?” We use lifetime history and the timing of onset to characterize regular smoking. We recognize that this single item does not differentiate between different styles or different amounts of smoking, both of which have genetic and environmental influences. Rather, we emphasize regular smoking because the relatively straightforward description of this variable coupled with the age ranges in this study increase the reliability of smoking recall for this important transition.
