Smoking, Lung Cancer, and Course-taking

In a 1996 article in the Journal of the American Statistical Association, Mitchell H. Gail quotes the 1964 Smoking and Health Surgeon General's Report regarding causal relationships:

Statistical methods cannot establish proof of a causal relationship in an association. The causal significance of an association is a matter of judgement which goes beyond any statement of statistical probability. To judge or evaluate the causal significance of the association between the attribute or agent and the disease, or effect upon health, a number of criteria must be utilized, no one of which is an all-sufficient basis for judgement.

As Gail wrote, the Surgeon General's Report defined those criteria as:

• consistency of the association in study after study
• strength of the association
• temporal pattern with exposure preceding disease
• coherence of the causal hypothesis with the body of evidence

While there's much to add to that list of criteria and much to comment on, the underlying notion that identifying a causal relationship is "a matter of judgement" is a salient one. And a list of criteria to guide that judgement is a powerful tool for anybody thinking about drawing causal inferences from a study.

Some time down the road it might be useful to compare the causal relationship discussion in the Surgeon General's Report to classic Cambell & Stanley description of internal and external validity published the year before (1963).

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Gail, M. H. (1996). "Statistics in Action," Journal of the American Statistical Association, Vol. 91, No. 433, pp. 1-13.

U.S. Department of Health, Education and Welfare, Public Health Services (1964), Smoking and Health; Report of the Advisory Committee to the Surgeon General of the Public Health Service, Public Health Service Publication No. 1103, Washington, DC: U.S. Government Printing Office.