A critical reassessment of the evidence bearing on smoking as the cause of lung cancer.

Since population statistics have contributed significantly to the belief that cigarette smoking is a cause of lung cancer, perhaps one should start by asking how population surveys and statistical studies can contribute to the understanding of the possibly complex causes of lung cancer or, in fact, any cancer? This question is basic since it includes cigarette smoking as one of the possible antecedents but does not ignore the rich evidence implicating others. If it is true that existing population studies clearly indicate that cigarette smoking is the major cause of lung cancer, then additional large and expensive population surveys to uncover other causes may not be warranted. On the other hand, if this general conclusion is not acceptable, then the groundwork may be laid for a much more inclusive population study. It is generally believed that existing evidence has established that smoking is a major cause of lung cancer. This report has undertaken to probe this belief - not to provoke or to please, but to dissect and to analyze. Because one adopts an analytical attitude, it may be difficult to avoid the impression that the focus of this paper is on the critical side. The voluminous research on smoking and lung cancer contains many good as well as bad points. While a critical analysis tends to bring out inadequacies, this should not be taken to imply that none of the past studies are of value. Quite to the contrary: many able investigators have studied this difficult problem with great care and have gathered valuable data, and their analyses have significantly contributed to the understanding of human disease. A critical analysis offers an objective framework for evaluating widely used research methods and analytic procedures but, unfortunately, without singling out individual good or bad points or emphasizing how the work of many of these scientists has enriched our knowledge. Bearing in mind these limitations, there is yet one other pressing need to closely analyze the statistical studies and population surveys of the effects of smoking. Unfortunately, conventional procedures based largely on animal studies are becoming increasingly inadequate for determining the toxicity of any consumed product or of a widespread pollutant. Continuing surveys of human populations may be the major method for monitoring the health of large communities and protecting men from the untoward effects of the byproducts of his many activities. The smoking and health population studies form a model on how such surveys may be conducted. If this model is invalid and possibly leads to misleading conclusions, as many respected statisticians and scientists have claimed, then incalculable damage may result in the long run if the shortcomings in this model are not made public.