Validity of self-reported passive smoking evaluated by comparison with smokers in the same household.

Validity of self-reported passive smoking among nonsmokers was evaluated by comparing it with data from smokers in the same household. Eight hundred and ninety-four males and 990 females responded to a lifestyle survey for a cohort study. Subjects consisted of all members aged 20 years or older in each household. One hundred and thirty-six males and 692 females nonsmokers within this group were examined for self-reported passive smoking. It should be noted that guests' smoking was also considered because the question about passive smoking included that when guests visited although guests' smoking could not be evaluated. Four percent of nonsmokers who reported passive smoking almost every day lived in households without smokers. This value was considered a misclassification of negative passive smoking as positive unless these subjects were visited by smoking guests almost every day. Eight percent of nonsmokers who reported no passive smoking had a spouse who smoked and 18% of these subjects also had other smokers in the same household. The misclassification rate for positive passive smoking as negative was thought to be 8% or higher although it was possible that the smoking spouse smoked only outside the home and that household members may live in different structures at the same site. The validity was thought to be fair in comparison with similar previous studies in Western countries.