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\noindent
\textit{British Medical J.}, vol.\ II, p.\ 43, 6 July 1957
and vol.\ II, pp.\ 297--298, 3 August 1957.
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\Huge{269--270}
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\Large{ALLEGED DANGERS OF CIGARETTE-SMOKING}
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\noindent
Your annotation on ``Dangers of
Cigarette-smoking''\footnote{\textit{British Medical Journal}, June 20,
p.\ 1518.} leads up to the demand that these hazards ``must be brought
home to the public by all the modern devices of publicity''. That is
just what some of us with research interests are afraid of. In recent
wars, for example, we have seen how unscrupulously the ``modern devices
of publicity'' are liable to be used under the impulsion of fear; and
surely the ``yellow peril'' of modern times is not the mild and soothing
weed but the original creation of states of frantic alarm.
A common ``device'' is to point to a real cause for alarm, such as the
increased incidence of lung cancer, and to ascribe it urgent terms to
what is possibly an entirely imaginary cause. Another, also illustrated
in your annotation, is to ignore the extent to which the claims in
question have aroused rational scepticism. The phrase ``in the presence
of the painstaking investigations of statisticians that are seen to have
closed every loophole of escape for tobacco as the villain of the
piece'', seems to be pure political rhetoric, even to the curious
practice of escaping through loopholes. I believe I have seen the
sources of all the evidence cited. I do see a good deal of other
statisticians. Many would still fell, as I did about five years ago,
that a good \textit{prima facie} case had been made for further
investigation. None think that the matter is already settled. The
further investigation seems, however, to have degenerated into the
making of more confident exclamations, with the studied avoidance of the
discussion of those alternative explanations of the facts which still
await exclusion.
Is not the matter serious enough to require more serious treatment?
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\noindent
In the \textit{Journal} of July 20 Dr.\ Robert N.\ C.\ McCurdy writes:
``Fisher's criticism\footnote{\textit{British Medical Journal}, July 6,
p.\ 43.} \dots would not be so unfair if he had specified what
alternative explanations of the facts still await exclusion''. I had
hoped to be brief. A few days later the B.B.C.\ gave me the opportunity
of putting forward examples of the two classes of alternative theories
which any statistical association, observed without the predictions of a
definite experiment, allows---namely, (1) that the supposed effect is
really the cause, or in this case that incipient cancer, or a
pre-cancerous condition with chronic inflammation, is a factor in
inducing the smoking of cigarettes, or (2) that cigarette smoking and
lung cancer, though not mutually causative, are both influenced by a
common cause, in this case the individual genotype.
The latter unexcluded possibility was known to Dr.\ McCurdy but he
brushes it aside with abundant irony. Is he really persuaded that this
is the way to arrive at scientific truth? Dr.\ McCurdy points out
correctly that difference in the genotypic composition of the smoking
classes---non-smokers, cigarette smokers, pipe smokers, etc., would not
explain the secular change in lung cancer incidence. I have never
thought that it would be charged with this task. Is it axiomatic that
the differences between smoking classes should have the same cause as
the secular change in incidence? Is there the faintest evidence to
support this view? Indeed, Dr.\ McCurdy's belief that cigarette smoking
causes lung cancer would be more secure if he did not consider it with
the \textit{non-sequitur} that increase of smoking is the cause of
increasing cancer of the lung. For at this point there appears one of
those massive and recalcitrant facts which have been emerging through
the smoke screen of propaganda. When the sexes are compared it is found
that lung cancer has been increasing more rapidly in men relative to
women. The absolute rate of increase is, of course, obscured by
improved methods of diagnosis, and by the increased attention paid to
this disease, but the relative proportionate changes in men and women
should be free from these disturbances, and the change has gone
decidedly against the men. But it is notorious, and conspicuous in the
memory of most of us that over the last fifty years the increase of
smoking among women has been great, and that among men (even if
positive) certainly small. The theory that increased smoking is ``the
cause'' of the change in apparent incidence of lung cancer is not even
tenable in face of this contrast.
For the secular change, therefore. neither the smoking causation theory
nor the theory of differential genotype will afford an explanation. For
the contrast between cigarette smokers and non-smokers both are
available; for the contrast between cigarette smokers and pipe smokers
the first theory requires some special pleading, but this has never been
lacking. The two circumstances (1) that heavy smokers show a greater
effect than light smokers, and (2) that persons who have voluntarily
abandoned smoking react like non-smokers or light smokers, are not
independent experimental confirmation of the smoking theory. They are
only reiteration of the main association to be explained. Any theory
which explains this association may be expected to explain these facts
also.
Differentiation of genotype is not in itself an unreasonable
possibility. Indeed strains of mice if genotypically different almost
invariably show differences in the frequency, age-incidence and type of
the various kinds of cancer. In Man cancer of the stomach has been
shown to be favoured by the gene for the blood group A. My claim,
however, is not that the various alternative possibilities which have
been excluded all command instant assent, or are going to be
demonstrated. It is rather that excessive confidence that the solution
has already been found is the main obstacle in the way of such more
penetrating research as might eliminate some of them. I am sure it is
useless to treat the question as though it were a matter of loyalty to a
political ideology or of forensic disputation. Statistics has gained a
place of modest usefulness in medical research. It can derive and
retain this only by complete impartiality, which is not unattainable by
rational minds. We should not be content to be ``not so unfair'', for
without fairness the statistician is in danger of scientific errors
through his moral fault. I do not relish the prospect of this science
being now discredited by a catastrophic and complacent howler. For it
will be as clear in retrospect, as it is now in logic, that the data so
far do not warrant the conclusions based upon them.
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\textit{British Medical J.}, vol.\ II, p.\ 43, 6 July 1957
and vol.\ II, pp.\ 297--298, 3 August 1957.
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