Passive smoking

Editor—The study by Enstrom and Kabat has a major flaw,¹ and I urge the editors of the BMJ to consider a retraction. The study assumes a considerable difference in the exposure to environmental tobacco smoke of never smokers' spouses compared to ever smokers' spouses. This is obviously wrong.

Most never smokers' spouses would have been exposed to considerable environmental tobacco smoke before the late 1990s when Californian public places became smoke-free. Thus for most of the study period, assuming the spouses are together for two to four waking hours a day, the comparison is eight to10 hours' exposure to tobacco smoke among spouses of never smokers and 12 hours' exposure to tobacco smoke among spouses of ever smokers. Assuming passive smoking increases mortality by 30%, the demonstrable difference between the groups would be about 5% ((12 – 10)/12)×30). This would be further reduced because of quitters among ever smokers and occasional smokers among never smokers. A 5% difference is extremely difficult to show in an epidemiological study, and inability to find a difference cannot be taken as absence of a difference.

However flawed this study, unless it is retracted by the BMJ the tobacco industry will use it to promote their vigorous opposition to antismoking legislation in general, and anti-environmental tobacco smoke laws in particular, creating controversy where there isn't any. Of course they have an urgent and ongoing need to replace loss of their customer base—10 000-20 000 lives per day— with new recruits of young smokers.