The criteria used to define current smokers, former smokers, and those who had never smoked cigarettes in the various cohorts are described in the Supplementary Appendix. In CPS I and CPS II, we used only the information about smoking obtained at the time of enrollment, whereas in the contemporary cohort studies, we used updated information when available in time-dependent analyses. The frequency of updating varied across cohorts. Analyses of former smokers were restricted to those who had quit 2 or more years before the start of follow-up.
