The distributions of the smoking behaviors and demographic covariates included in the analysis of the NHS and PLCO datasets are presented in Table 1. The men in the PLCO sample have smoking behaviors that are more prevalent and more severe (greater frequency of ever, current and heavy smokers, earlier age of onset, longer duration, and greater pack-years) than do the women in the NHS sample. The direction and significance of correlations among the smoking phenotypes within the dataset are similar, with all correlations highly significant (P<0.0001), except for the correlation between age at initiation and cigarettes per day in the NHS sample (Table S2).
