Mortality in Cigarette Smokers and Quitters

THE health benefits of quitting cigarette smoking have usually been inferred from the differences in morbidity and mortality experienced by smokers and ex-smokers.1 2 3 When formal observation of these groups begins, the ex-smokers have quit smoking at various times in the past; thus, it is not usually possible to assess their health-related characteristics at a time when they were smoking. Consequently, it is difficult to be certain that quitting itself and not some other difference or differences between quitters and persistent smokers has been responsible for the apparently better health outcome.In an earlier study4 longitudinal data derived from three or . . .