So why was Bailar, a respected expert on the analysis of medical studies, so sceptical?
A back-of-the-envelope calculation explains his concern. People who smoke 20 cigarettes a day face a 75 to 80 per cent higher risk of developing heart disease than nonsmokers, and studies suggest that passive smokers breathe in about 1 per cent of the amount inhaled by direct smokers. As such, they should also face about 1 per cent of the extra heart disease risk faced by smokers. In other words, just 075 per cent-more than 30 times lower than the figure found by Jiang He and his colleagues.
This huge discrepancy is dividing medical scientists into two camps. On one side are those who believe it reveals the existence of a highly non-linear effect of tobacco smoke on the body, where just a whiff can trigger a dramatic increase in risk.
On the other side are those who, like Bailar, suspect the discrepancy highlights fundamental flaws in the methods used to assess the risks from passive smoking. Some go further, arguing that in the drive to discourage smoking, implausible results are not being questioned as rigorously as they should.
No one is accusing Jiang He and his colleagues of shoddy research. Even
Bailar concedes that their meta-analysis of 18 studies is up to scratch. What
worries him is whether even the best meta-analysis is capable of reliably
detecting small risks. In his editorial, Bailar argues that there are many ways
in which a meta-analysis of passive smoking studies can give spuriously high
ris
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Contact: Claire Bowles
claire.bowles@rbi.co.uk
44-171-331-2751
New Scientist
26-May-1999