When results look too good to be true, they probably are
As a cancer researcher who has published extensively on the harmful
effects of smoking, I am in favor of vigorous smoking bans and feel there
is no justification for nonsmokers to have to breathe air polluted with
tobacco smoke. However, the study by Sargent et al. claiming that the 6
-month smoking ban in Helena, Montana was associated with a drop in heart
attacks must be viewed with skepticism.
The authors reported that the number of heart attacks within the city
of Helena dropped by 40% immediately following the initiation of the ban.
They claim that this is powerful evidence for an effect of exposure to
secondhand smoke on heart attacks. But if we look at their data we see
just how questionable this claim is.
First, the researchers only had information from hospital records on
where a person lived. They did not interview the patients, so they had no
information on whether their exposure to secondhand smoke changed as a
result of the ban. They also did not present any information on whether
smoking habits were affected by the ban. The fact that they had no
information on exposure is a major deficiency.
Second, the drop in heart attacks is based on very few cases: 4 per
month on average during the ban compared to 7 per month before. Due to
these small numbers the reported difference could easily be due to chance
or to some uncontrolled factor. The number of heart attacks in the area
outside Helena was even smaller. It should not be surprising that, given
these small numbers, there are fluctuations of the magnitude seen in this
study.
Finally, the “immediate effect” and its magnitude really should make
anyone stop and question the connection the authors are asserting. There
are few interventions in public health that have such an immediate effect.
Even if all active smokers in Helena had quit smoking for at least a year,
one would not expect to see such a dramatic effect. No previous
epidemiologic study or community smoking cessation program has ever shown
that a reduction in smoking or exposure to secondhand smoke causes an
immediate decline in heart disease incidence or mortality.
A rigorous study would have involved collecting information on a
population of adequate size and interviewing individuals to assess their
pre-existing risk for heart disease as well as how their behavior was
affected by the ban in order to make a plausible connection between the
two phenomena.
The attempt to make claims about the effects of smoking bans based on
this very weak ecologic study raises disturbing questions about our
ability to distinguish between sound science and wishful thinking.
Rapid Response:
When results look too good to be true, they probably are
As a cancer researcher who has published extensively on the harmful
effects of smoking, I am in favor of vigorous smoking bans and feel there
is no justification for nonsmokers to have to breathe air polluted with
tobacco smoke. However, the study by Sargent et al. claiming that the 6
-month smoking ban in Helena, Montana was associated with a drop in heart
attacks must be viewed with skepticism.
The authors reported that the number of heart attacks within the city
of Helena dropped by 40% immediately following the initiation of the ban.
They claim that this is powerful evidence for an effect of exposure to
secondhand smoke on heart attacks. But if we look at their data we see
just how questionable this claim is.
First, the researchers only had information from hospital records on
where a person lived. They did not interview the patients, so they had no
information on whether their exposure to secondhand smoke changed as a
result of the ban. They also did not present any information on whether
smoking habits were affected by the ban. The fact that they had no
information on exposure is a major deficiency.
Second, the drop in heart attacks is based on very few cases: 4 per
month on average during the ban compared to 7 per month before. Due to
these small numbers the reported difference could easily be due to chance
or to some uncontrolled factor. The number of heart attacks in the area
outside Helena was even smaller. It should not be surprising that, given
these small numbers, there are fluctuations of the magnitude seen in this
study.
Finally, the “immediate effect” and its magnitude really should make
anyone stop and question the connection the authors are asserting. There
are few interventions in public health that have such an immediate effect.
Even if all active smokers in Helena had quit smoking for at least a year,
one would not expect to see such a dramatic effect. No previous
epidemiologic study or community smoking cessation program has ever shown
that a reduction in smoking or exposure to secondhand smoke causes an
immediate decline in heart disease incidence or mortality.
A rigorous study would have involved collecting information on a
population of adequate size and interviewing individuals to assess their
pre-existing risk for heart disease as well as how their behavior was
affected by the ban in order to make a plausible connection between the
two phenomena.
The attempt to make claims about the effects of smoking bans based on
this very weak ecologic study raises disturbing questions about our
ability to distinguish between sound science and wishful thinking.
Competing interests:
None declared
Competing interests: No competing interests