The assessment of exposure to environmental tobacco smoke

This paper examines the manner in which assessments of exposure to environmental tobacco smoke (ETS) are used in epidemiological studies seeking to establish an association between such exposure and diseases such as lung cancer. Two such studies are described. A review of the literature shows that exposure to ETS is not accurately measured by subjective evaluations communicated via questionnaire. The inaccuracy is evident in situations where recent exposure is being measured and may reasonably be expected to be even greater when long-term exposure is at issue. Such inaccuracies do not necessarily invalidate the conclusions that may be drawn from a case/control study. In a situation where all types of errors occur equally frequently among cases and controls, the effects of such errors are to lower the relative risk estimate, to reduce the power of the study, and to make it more difficult to establish an association between exposure and disease. However, in a situation where the pattern of errors is different for cases than it is for controls, there is considerable potential for the errors to produce misleading conclusions. Increased concentration on the validation of subjective ETS exposure assessments is recommended. Copyright (C) 1997 Elsevier Science Ltd.