Ever smoking cigarettes was defined by a positive response to the question, `did you ever try smoking cigarettes'. Regular smoking was defined as having smoked 21 or more cigarettes over the lifetime and smoking three or more times per week for a minimum of three weeks. This intensity of smoking is associated with loss of control over cigarettes, ND and withdrawal in young smokers (DiFranza et al. 2007) and was appropriate in this young cohort where 22% were under age 18. The Fagerstrom Test for Nicotine Dependence (FTND) was used to define ND (Fagerstrom 1978; Heatherton et al. 1991) for all offspring who were regular smokers. Offspring with a value of 4 or greater on the FTND were defined as ND. From these data we created a four level categorical variable for offspring smoking: never smoker, ever smoked, regular smoker and ND.
