Evidence and The Process of Reasoning

Cigarette, Cancer and Statistics

Sir Ronal Fisher, 1958

...I have been concerned with the problem of how experimentation should be carried out, how reasoning processes should be applied to the data supplied by experimentation or by survey so as to give really conclusive answers.

.....So our evidence about inhaling is embarrasing and difficult. There is no doubt that inhaling is more common among heavy cigarette smokers than among light cigarette smokers in Great Britain, where inhaling isnot nearly a universal practice. There is no doubt that cancer is commoner among the heavy cigarette smokers than among the light cigarette smokers. Consequently, if inhaling had no effect whatever, you would expect to find more inhalers among the cancer patients than among the non-cancer patients. There would be an indirect correlation through the association of both with the quantity smoked. Now, of course, in what was reported everything was thrown together; and yet, in the aggregate data, it appeared that the cancer patients had the fewer inhalers than the non-cancer patients. It would look as though, if one could make the inquiry by comparing people who smoke the same number of cigarettes, there would be a negative association between cancer and inhaling. It seems to me the world ought to know the answer to that question. Before I stop, in fact, I hope I shall make clear that there is a case for further research, and I shall only mention two areas which would seem to be profitable for investigation. I would stress the importance of what could be done comparatively easily with rather little expense, namely, to ascertain unmistakably what the facts are about inhaling. If inhaling is found to be strongly associated with lung cancer, it would be consonant with the view that the products of combustion, wafted over the surface of the bronchus, might induce a precancerous and thence a cancerous condition. But if there is either no association at all or a negative association, we should have to reject altogether that simple theory of the causation of cancer.

The subject is complicated, and I mentioned at an early stage that the logical distinction was between A causing B, B casing A, something else causing both. Is it possible, then, that lung cancer – that is to say, the precancerous condition which must exist and is known to exist for years in those who are going to show overt lung cancer – is one of the causes of smoking cigarettes? I don’t think it can be excluded. I don’t think we know enough to say that it is such a cause. But the precancerous condition is one involving a certain amount of slight chronic inflammation. The causes of smoking cigarettes may be studied among your friends. To some extent, and I think you will agree that a slight cause of irritation – a lsight disappointment, an unexpected delay, some sort of a mild rebuff, a frustration- are commonly accompanied by pulling out a cigarette and getting a little compensation for life’s minor ills in that way. And so, anyone suffering from a chronic inflammation in part of the body (something that does not give rise to conscious pain) is not unlikely to be associated with smoking more frequently, or smoking rather than not smoking. It is the kind of comfort that might be a real solace to anyone in the fifteen years of approaching lung cancer. And to take the poor chap’s cigarettes away from him would be rather like taking away his white stick from a blind man. It would make an already unhappy person a little more unhappy than he need be.

...There is the attitude of a man (may I say, I think it is an entirely rational attitude and one within his own competence to judge) who says, 'There seems to be some danger - I cant assess whether it is infinitesimal or serious. This habit of mine of smoking isnt very important to me. I will give up smoking as a kind of insurance against a danger which I am quite unable to assess.' That seems to me a perfectly rational attitude. What is not quite so much the work of a good citizen is to plant fear in the minds of perhaps a hundred million smokers throghout the world - to plant it with the aid of all the means of modern publicity backed by public money, without knowing for certain that they have anything to be afraid of in the particular habit against which thepropaganda is to be directed. After all, a large n umber of the smokers of the world are not very clever, perhaps not very strong-minded. the habit is an insidious one difficult to break, and consequently in many, many cases there would be implanted what a psychologist might recognizze as a grave conflict.


Sir Ronal Fisher, 1958
http://www.york.ac.uk/depts/maths/histstat/fisher272.pdf


"Love is most nearly itself when here and now cease to matter".
T.S. Eliot