which the data were censored, or until December 31, 2011, whichever was earliest. Deaths and
person-years were tabulated according to smoking status and 10-year attained-age groups, and
overall mortality was standardized to the age
distribution in the U.S. population in 2000. We
calculated the proportional contribution of each
disease to the total excess risk of death among
current smokers as compared with persons who
never smoked. We used Cox proportional-hazards
regression with adjustment for age and cohort to
estimate pooled relative risks among current and
former smokers as compared with those who
never smoked, using the stratified Cox procedure and further adjusting for race, educational
level, and daily alcohol consumption by including variables for these factors in the model. For
secondary analyses, we used Cox models with
time-dependent variables for number of cigarettes
per day among current smokers and number of
years since cessation among former smokers.
We calculated P values for trend by modeling a
continuous variable for number of cigarettes per
day (among only current smokers) and number of
years since cessation (among only former smokers).