National incidence of smoking and misclassification among the U.S. married female population

Because of a lack of representative data on smoking status misclassification among U.S. married females, a two-part study was conducted. Part I was conducted to obtain nationally representative estimates of the percentage of U.S. women who report themselves to be current, former, and never smokers, to determine the concordance of smoking habits among spouse pairs, and to establish field quotas and probability weightings for Part II. Part II was conducted to determine smoker misclassification rates using salivary cotinine as an indication of active smoking. Part I, conducted in January 25-29, 1992, utilized random-digit dialing telephone interviewing throughout the 48 contiguous United States. Part II, conducted from February 19, 1992 to March 7, 1992, was a mall-intercept study in nine geographically disperse U.S. cities and it involved interviewing and saliva collection. Among married U.S. women, 25% reported they were current smokers, 22% reported they were former smokers, and 53% reported they were never smokers. Using a cotinine concentration of either > 35 ng/ml or > 106 ng/ml to indicate regular smoking, 3.61% and 2.55% of regular smokers, respectively, reported themselves to be never smokers. The concordance ratio, an important parameter in correcting for non-differential misclassification bias, was found to be 5.52. In addition, an indication of substantial differential misclassification was found between exposed and unexposed populations. This type of misclassification bias has previously not been accounted for in the adjustment of epidemiology-based risk assessments of tobacco smoke exposure and lung cancer. Taken together, these data suggest that misclassification bias alone is likely to explain any lung cancer risk elevation observed in the U.S. epidemiology of environmental tobacco smoke exposure among nonsmoking women.