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Hackshaw et al. estimated that adjustment for bias due to misclassification of smoking habits reduces the observed relative risk of lung cancer in non-smoking women associated with smoking by the husband from 1.24 to 1.18. This bias estimate is little affected by using an alternative method for misclassification adjustment or by using updated data from 47 studies rather than data from the 37 studies used by Hackshaw et al. The bias is increased if strong evidence of much higher misclassification rates in Asian women is taken into account and could then explain about half the observed association. Misclassification correction has not previously been attempted for dose-response data. We describe a suggested approach and apply it to data relating risk to amount smoked by the husband. As shown in paper II of this series the unadjusted increase in risk per 10 cigarettes/ day smoked by the husband is 10% (95% CI 5 to 15%), reducing to either 6% (95% CI 1 to 11%) or 9% (95% CI 5 to 14%) after adjustment for confounding by fruit, vegetable and fat consumption and education using respectively unweighted or weighted means to combine evidence on the ETS/confounder association from different studies. Further adjustment for plausible levels of misclassification similarly reduced these two estimates to, respectively, 2% (95% CI -3 to 8%) or 5.5% (95% CI 0 to 11%). Difficulties in applying misclassification bias corrections are discussed. Other sources of bias will be considered in later papers in this series.

Copyright © 2002 S. Karger AG, Basel

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