MISCLASSIFICATION OF SMOKING IN A FOLLOW-UP POPULATION STUDY IN SOUTHERN GERMANY

Smoking prevalence in southern Germany was studied in 1984-1985 using a representative cohort of 4022 subjects aged 25 to 64 years, with 375 3 reinterviewed in 1987-1988. Data were available for analysis from in terviews on self-reported smoking behavior and from serum cotinine mea surements in both investigations. More men than women reported current smoking, and particularly heavy smoking. Serum cotinine levels increa sed steadily with the daily number and nicotine yield of cigarettes sm oked. Mean cotinine levels in ex-smokers were higher than those in nev er smokers, suggesting that a higher percentage of current smokers are misclassified as ex-smokers than never smokers. Using cotinine rather than self-reported smoking data increased the proportion of true smok ers in the subgroup of self-reported smokers by about 3% in males and by about 1% in females. Data from the reinterviews revealed that repor ted smoking status confirmed by cotinine measurement in 1987-1988 conf licted in a number of cases with the data obtained in 1984-1985 using the same procedure. For example, 0.1% of those who stated they were cu rrent regular smokers, 4.3% of those who stated they were current occa sional smokers, and 17.6% of those who stated they were ex-smokers in 1984-1985 claimed in 1987-1988 to have never smoked. This misclassific ation of ex-smokers was higher in women. Altogether the true proportio n of ex-smokers among self-reported never smokers was about 9.7% (17.8 % in men and 6.7% in women). The widely variable uptake of tobacco smo ke by smokers, as well as the misclassification of true smokers and ex -smokers as never smokers, needs to be considered in epidemiological s tudies evaluating the health risks from both active and passive smokin g. (C) 1998 Elsevier Science Inc.