Smoking and Tobacco Control Monograph No. 7 
These are not biomarker data, so there is no inference in these particular 
subjects as to what the level of nicotine or carbon monoxide may have 
been. The question is, again, looking at the yield or brand as an estimate of 
exposure, there was simply no relationship observed in these observational 
studies. 
DR. HUGHES: In most of these studies, the control group is labeled 
nonsmokers. Is that usually never-smokers? 
DR. SAMET: In most of the studies that are labeled nonsmokers, that is 
a never-smoker group. You basically will see two contrasts: vs. never- 
smokers or, in some of the studies, the contrast has been made between 
sort of the lower exposure group vs. the higher exposure group. 
DR. HUGHES: The reason 1 asked that is, it seems to me that using controls 
of ex-smokers would be important for two reasons. One, it would be a 
control for the confounds that Dr. Woosley mentioned earlier. Second, 
all your studies have to do with switching cigarettes. None of them has 
to do with the alternative of either quitting or switching to a low-nicotine 
cigarette. Are there data to inform the consumer of the question, how much 
do 1 want to improve my health by quitting, vs. how much do 1 improve my 
health by switching to a low-tar cigarette? 
DR. SAMET: Certainly, there are abundant data on how risks of diseases vary 
following cessation. 1 do not want to complicate this, and it was the subject 
of the 1990 Surgeon General's report. These risks vary in complex ways for 
different diseases, depending on the age at which the smoker stopped 
smoking and the duration of successful abstinence from smoking. 
So, it is somewhat difficult to capture a single number that describes the 
risk in ex-smokers. It has to be done in a far more complex way. But, on 
the other hand, there are data sets, like the American Cancer Society data 
sets, that would allow one to describe how risks change following smoking 
cessation, for example. And it would be possible to derive some quantitative 
contrast between what might happen to smokers of different ages, different 
prior smoking histories, with switching products vs. cessation. 
DR. RICKERT: On your emphysema slide, the one that dealt with the 
changes in lung function, there was a label that said, "never smoked and 
not susceptible to the effects of tobacco smoke." Do you have any idea 
what proportion of the population of smokers fell into the category "not 
susceptible"? 
DR. SAME'!’: Such numbers are not readily available. 1 think most people 
who work in this field would guess that with regard to COED, perhaps 20 to 
25 percent of continued smokers seemed to fall into this grouj) of ra[)id lung 
function decline. 
DR. RICKER T: Are there any |)ostulated mechanisms why smokers should 
be in that grou[)? 
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