Siegel states, "That suggests that smoking is associated with other types of health behaviors that are affecting the outcome. When other health behaviors were included, it completely wiped out the effect of smoking." [HHS] Spiegel also saw that the researchers’ results found that former-smokers performed better on the memory tests than smokers. He stated, "The reason their memory is better is not because they smoked -- that's not plausible.” [HHS]

He argues that former smokers or non-smokers may just have better overall health habits than smokers; may be better educated; or have naturally better cognitive levels.

As reported by the article from the HHS, Dr. Norman H. Edelman, a scientific consultant to the American Lung Association, summarizes: "This study is generally a confirmation of previous work. But there is a fundamental question: Are they stupid because they smoke or do they smoke because they are stupid?"