Berlin, Germany
To the Editor:
In a recent article by Kawachi et al,1 the
differing prevalence of cardiovascular risk factors and
other lifestyle variables in women with and those without tobacco
smoke exposure is attributed to the lower socioeconomic status of the
female passive smokers. In order not to impute the socially determined
elevated coronary heart disease (CHD) risk to the passive
smokers, the authors adjusted their data by standardizing for these
factors. In so doing, however, they may have compounded another error,
casting serious doubt on the validity of their results. They overlooked
the fact that women from lower social classes in general pay far less
attention to their health and visit their doctors less frequently than
do women from higher social classes. This is particularly true in the
United States, where financial reasons also play a role. The exclusion
of about 3500 women with a history of CHD before the study commenced,
as well as the exclusion of an unspecified number of women with CHD in
the course of the study inevitably led to a higher prevalence of
undiagnosed CHD cases in the group of passive smokers, so that it is
really not surprising that a higher incidence of myocardial infarction
was found in the women exposed to tobacco smoke. Given the selection
bias, however, a causal relation is not substantiated in this
study.
Selection bias is supported also by another finding reported in the
article by Kawachi et al. Tobacco smoke exposure at the workplace must
have decreased during
© 1998 American Heart Association, Inc.
Correspondence
Passive Smoking and Coronary Heart Disease in Women