The following question was used to assess the current number of cigarettes smoked each day: In the past 30 days, on those days when you smoked, on average, how many cigarettes did you smoke per day? The number of cigarettes was recorded and standardized (z-score) to create a quantitative measure of cigarettes smoked per day. All subjects were asked whether they had ever smoked cigarettes on at least some days, in their lifetime. Individuals who had never smoked in their lifetime (41.8%) were excluded from further analyses.
