Self-reported number of cigarettes smoked per day was available from at least one exam for 2883 participants. The quantitative trait maximum number of cigarettes per day represented the largest number of cigarettes smoked per day reported by each participant at any point throughout the study; this value was equal to zero for individuals who reported smoking no cigarettes at each exam. Skewness and kurtosis for maximum number of cigarettes per day were 1.0 and 3.7, respectively (excluding non-smokers these were 0.8 and 4.3, respectively). A variety of transformations were used on the trait; however, because none markedly reduced skewness or kurtosis, analyses were performed on untransformed values. Covariates for some analyses included sex and the age and year at which the maximum number of cigarettes were smoked. These age and year variables were the first age and year at which the person reported smoking that quantity (including zero for non-smokers) if it was reported more than once.
