Reanalysis of epidemiological evidence on lung cancer and passive smoking

doi:10.1136/bmj.320.7232.417

BMJ 2000;320:417-418 ( 12 February )

Papers

Reanalysis of epidemiological evidence on lung cancer and passive smoking

J B Copas, professor, J Q Shi, research fellow.

Department of Statistics, University of Warwick, Coventry CV4 7AL

Correspondence to: J B Copas jbc{at}stats.warwick.ac.uk

Objective: To assess the epidemiological evidence foran increase in the risk of lung cancer resulting from exposureto environmental tobaccosmoke.
Design: Reanalysis of 37 published epidemiologicalstudies previously included in a meta-analysis allowing for thepossibility of publicationbias.
Main outcome measure: Relative risk of lung cancer among femalelifelong non-smokers, according to whether her partner was a currentsmoker or a lifelong non-smoker.
Results: If it is assumed that all studies that haveever been carried out are included, or that those selected forreview are truly representative of all such studies, then theestimated excess risk of lung cancer is 24%, as previously reported(95% confidence interval 13% to 36%, P<0.001). However, a significantcorrelation between study outcome and study size suggests thepresence of publication bias. Adjustment for such bias impliesthat the risk has been overestimated. For example, if only 60%of studies have been included, the estimate of excess risk fallsfrom 24% to 15%.
Conclusion: A modest degree of publication bias leadsto a substantial reduction in the relative risk and to a weakerlevel of significance, suggesting that the published estimateof the increased risk of lung cancer associated with environmentaltobacco smoke needs to be interpreted withcaution.

Key messages

A systematic review of epidemiological studies on passive smoking estimated the increased risk of lung cancer as 24%
There is clear evidence of publication bias in these studies
Reanalysis of the data allowing for the possibility of publication bias substantially lowers the estimate of relative risk

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Rapid Responses:

Read all Rapid Responses

Passive Smoking: Wrong end of the telescope?: Norbert Hirschhorn
bmj.com, 12 Feb 2000 [Full text]
Nothing new here: Stanton A Glantz
bmj.com, 12 Feb 2000 [Full text]
No unpublished studies on passive smoking in Hong Kong: T H Lam
bmj.com, 14 Feb 2000 [Full text]
Challenge to Professor T. H. Lam: Martha Perske
bmj.com, 15 Feb 2000 [Full text]
Passive smoking risks: over- or underestimated?: T L P Watts
bmj.com, 15 Feb 2000 [Full text]
Turning over the wrong stone: Kenneth C Johnson, et al.
bmj.com, 17 Feb 2000 [Full text]
Mooting the "Publication Bias" Issue: Leroy J Pletten
bmj.com, 24 Feb 2000 [Full text]
Unfair scales for a visual test of publication bias: Christopher Cates
bmj.com, 4 Mar 2000 [Full text]
Over-reliance on p values: Adam Jacobs
bmj.com, 25 Mar 2000 [Full text]
Few unpublished studies on passive smoking: Lisa Bero
bmj.com, 6 Apr 2000 [Full text]