Supplementary memorandum by Dr Allan Hackshaw
Royal College of Physicians (SP 50)
In response to answers given to certain questions
by Dr Steve Stotesbury of Imperial Tobacco Ltd (UK) to the Health
Committee, I felt it was necessary to provide further comment
on these issues to the Committee.
Q137. Dr Naysmith to Dr Stotesbury
Comment: Although many studies did not report
statistically significant results, most showed an increased risk
(for example, 47 out of 57 studies on lung cancer and ETS). The
lack of statistical significance was usually due to insufficient
numbers of subjects in a particular study. Combining the results
of all studies (using an established approach called "meta-analysis")
overcomes the problem of having small studies and produces unequivocal
conclusions, ie that ETS exposure is harmful.
Q141. Dr Naysmith to Dr Stotesbury
Comment: Dr Stotesbury referred earlier to "flawed"
evidence, yet quotes the Enstrom and Kabat paper as "a major
study of over 120,000 Californians over a 40-year period"
that reported risks that were "considerably weaker than generally
believed". This study was based on comparing the smoking
status of individuals married to non-smokers in 1959 with the
death rate from lung cancer and heart disease by 1998. However,
the study was conducted in California, which has the highest divorce
rate in the US and a high smoking quit rate, so within this 40-year
period many non-smokers who were exposed at the start will be
considerably less exposed during the study. This would produce
a spuriously weak risk. For example, a woman in the study who
was married to a smoker in 1959 but divorced him in 1960 would
be treated in the 1998 analysis as if she were still married to
a smoker. However, her risk of lung cancer and heart disease due
to ETS during the 40-year period would be similar to that of a
woman who was unexposed, so it would be incorrectly concluded
that ETS exposure was not harmful or has a negligible effect.
Q147. Dr Stoate to Dr Stotesbury
Comment: The study by IARC 1998 included results
associated with exposure to ETS during childhood and the risk
of lung cancer in adulthood. The comments made by Dr Stoate referred
to childhood exposure and childhood diseases.