Smoking was categorized as ‘never’ (fewer than 100 cigarettes lifetime), ‘former’ or ‘active’ smokers in 1975. Further, if smoking status was unchanged at the 1981 assessment, participants were classified as ‘persistent never smokers’, ‘persistent former smokers’ or ‘persistent active smokers’. Participants who were active smokers in 1975 and former smokers in 1981 were classified ‘quitters’; those who were non-smokers in 1975 and smokers in 1981 were ‘initiators’. The category of ‘active’ smokers included both daily and non-daily smokers. Daily smokers reported number of cigarettes smoked per day (cpd) at each time point, and those who smoked >20 cpd were considered heavy smokers.
