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Passive smoking and lung cancer

BMJ 1998; 317 doi: (Published 01 August 1998) Cite this as: BMJ 1998;317:346

Strength of evidence on passive smoking and lung cancer is overstated

  1. Peter Lee, Independent consultant in statistics and epidemiology.*
  1. *Sutton, Surrey SM2 5DA zPeter Lee acts as a consultant to the tobacco industry
  2. Analytisch-biologisches Forschungslabor, D-80336 Munich, Germany
  3. Division of Environmental Epidemiology, Institute of Environmental Medicine, Karolinska Institute, Box 210, S-171 77 Stockholm, Sweden
  4. Department of Environmental and Preventive Medicine, Wolfson Institute of Preventive Medicine, St Bartholomew's and the Royal London School of Medicine and Dentistry, London EC1M 6BQ

    EDITOR—Hackshaw et al estimate a 26% excess risk of lung cancer (95% confidence interval 7% to 47%) in non-smokers who live with a smoker.).1 This estimate may be too high.

    Their adjustment for smoking misclassification bias is inadequate for two reasons. Firstly, it is based on the comparatively low misclassification rates seen in American and British populationsand ignores evidence of far higher rates in Asian women (table)24Secondly, it uses a new adjustment technique that takes no account of the varying relative risks from smoking in the 37 studies. Despite the fact that lung cancer has many known causes and the evidence that smoking and passive smoking are associated with higher exposure to many adverse lifestyle risk factors,).5 the authors' consideration of confounding is limited to fruit and vegetable consumption. The authors dismiss publication bias, using an argument that addresses only whether such bias might explain the whole observed association. They do not even mention recall bias, and they do not discuss implications of specific weaknesses of the studies. After their inadequate downward adjustment for bias and confounding, they adjust upwards for effects of non-spousal passive exposure to smoke. Such effects are inferred indirectly from cotinine data, and the direct evidence that exposure to smoke in the workplace, in social situation, and during childhood is not associated with risk of lung cancer is ignored.

    View this table:

    Rates of misclassification of smoking in Asian women

    Hackshaw et al also estimate an excess risk of 19% from passive smoking, by extrapolating from the risk in current smokers, and this may also be too high. The use of particulate matter rather than cotinine to calculate the relative exposure of passive and active smokers would reduce the excess risk estimate at least tenfold; allowance for a quadratic component to the dose-response wouldreduce …

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