Third, the rate of death from COPD continues to increase among both male and female smokers in contrast to a significant decrease in risk among men who never smoked. This increase is not simply a function of aging, since it affects male smokers 55 years of age or older and female smokers 60 years of age or older. Nor can it be explained by differences in the average duration of smoking or the number of cigarettes smoked per day, since daily consumption was actually lower in the contemporary cohorts than in the CPS II cohort, and the average duration of smoking did not change significantly at any age. The ability to diagnose COPD has improved over time,33 but this would probably affect the number of prevalent cases more than the number of deaths for which COPD is considered to be the underlying cause of death. A plausible explanation for the continuing increase in deaths from COPD among male smokers is that cigarettes marketed since the late 1950s have undergone design changes that promote deeper inhalation of smoke.34 For example, the
