A EUROPEAN VALIDATION-STUDY OF SMOKING AND ENVIRONMENTAL TOBACCO-SMOKE EXPOSURE IN NONSMOKING LUNG-CANCER CASES AND CONTROLS

Objectives: The purpose of this study was to validate, in a case-contr ol study, the reporting by lung cancer cases and controls of their own lifetime smoking habits and of the smoking habit of the spouse. Metho ds: In a multicenter (Sweden, Spain, Italy) case-control study of envi ronmental tobacco smoke (ETS) and lung cancer, subjects were screened by repeated probing to exclude regular smokers of one cigarette/day or more for one year or more, and to quantify any occasional smoking. We then performed a short validation interview with next-of-kin in three centers. Results: Only five of 408 index subjects who had never smoke d regularly (1.7 percent) were reported by next-of-kin to be former re gular smokers. These subjects had a cumulative lifetime consumption of cigarettes below 1.1 pack years. Among 351 subjects with quantitative smoking information from both sources who reported ever smoking 400 c igarettes or less (the definition of never-smoker used in the multicen ter ETS study), nine subjects (2.6 percent) had smoked more than this amount occasionally according to next-of-kin. Misclassification was no t higher for cases than controls. Relative risks for lung cancer assoc iated with indicators of ETS exposure were not substantially altered b y excluding the nine possibly misclassified subjects. The reports from 223 pairs of index subjects and next-of kin regarding the cumulative amount smoked by the spouse agreed quite well (Spearman's rank correla tion 0.75 for reported smokers, 0.92 for all subjects). Only one index subject failed to report a spouse who had smoked regularly (99 percen t sensitivity). Conclusions: Smoking status and exposure to spousal ET S as reported by lung cancer cases and controls agreed strongly with r eports by next-of-kin. Overall, our results suggest that bias from smo ker misclassification is likely to be insignificant, and they contribu te to the evidence linking exposure to ETS with an increased risk of l ung cancer.