From BMJ USA 2003;July:352

The article by Enstrom and Kabat (p 369) is the latest in a long series of publications funded by the tobacco industry that report little or no relationship between environmental tobacco smoke (ETS) and disease.1 The current study has an aura of legitimacy because it is drawn from the American Cancer Society (ACS) Cancer Prevention Study I (CPS-I), a landmark prospective study of the hazards of active smoking,2 and because the analyses are based on nearly 40 years of data. Despite these apparent strengths, the study by Enstrom and Kabat is uninformative and its conclusions are exaggerated.

Indeed, the negative conclusions were entirely predictable from the outset because of the flawed way in which exposure to ETS was classified. CPS-I collected no information on ETS exposure other than the smoking status of the spouse. The study began in 1959, an era in which secondhand smoke was pervasive; virtually everyone was exposed at work, in social settings, or in other activities of daily living. Enstrom and Kabat therefore could not identify a comparison group of “unexposed” persons. Their analyses essentially compare nonsmokers married to a smoking spouse to nonsmokers with other sources of ETS exposure. This potential for misclassification was further exacerbated in the final 26 years …