Promotion in Smoking Initiation

Causation can never be proven beyond question. The strongest evidence for causality comes from controlled experiments in which individuals are randomly assigned either to a group that will receive exposure to the causal agent—in this case, cigarette advertising—or to one or more control groups that are not exposed to the causal agent, but are identical to the exposure group in every other way. This kind of study is obviously impossible to arrange in the case of cigarette advertising and also for most other potentially harmful exposures of interest to public health professionals. However, even the randomized controlled trial, the sine qua non of scientific causal evidence, can allow for alternative explanations, and whole books have been written to enumerate the variety of threats to validity that can compromise interpretation of such trials (Campbell and Stanley, 1966; Kerlinger, 1985). The best that one can do is attempt to build a body of evidence that supports a causal inference.