Friday, 10 December 2010

Bertrand Russell On Smoking

The London Hospitals study was the first British study to investigate possible causes of the growing epidemic of lung cancer. It was published by Richard Doll and Bradford Hill in 1950. Bradford Hill was a statistician, and Richard Doll was a young doctor. In the study, several hundred lung cancer patients in London hospitals were questioned about their past smoking habits and other behaviours, to see whether any pattern emerged.

Many years later, Sir Richard Doll wrote:

By the time we had data on several hundred patients it was obvious that the principal difference between the patients with and without lung cancer was their smoking habits, and we had to make up our minds whether the association was due to chance, bias, confounding, or to cause and effect. The evidence that led us to conclude that it was due to the last (and which led me to give up smoking in 1949) is described in our first paper... (source)

In fact, the results eventually showed that in 649 cases of lung cancer, 647 were among smokers. . . .

. . . It certainly looked like a very strong case had been made. The lung cancer patients were almost all smokers. It very much looked as if it was smoking that was causing lung cancer. Richard Doll clearly thought so, since he promptly gave up smoking. It also appeared to have convinced Sir George Godber:

Almost half a century ago we learned that smoking was the main cause of lung cancer. Albeit our knowledge in 1950 was so limited,... (source)

Godber was later to become one of the principal instigators of the notion of passive smoking - the idea that smokers not only harmed themselves, but also the people around them. . . .

. . . we ought to ask of the London Hospitals study what fraction of its overall sample population were smokers, for this would give the fraction of lung cancer patients that might be expected to be smokers, if smoking carried no risk.

And this figure is available in Table 4 of the study. There were 2 non-smokers and 647 smokers in the lung cancer study group. And there were 27 non-smokers and 622 smokers in the non-lung-cancer control group. So that, in the study as a whole, 97.7% of patients were smokers. This being so, we would expect that 97.7% of lung cancer patients would also be smokers, if smoking was unconnected to lung cancer. Instead we find that 99.7% of them were smokers. Is that particularly alarming? All we have discovered is that in a population in which nearly everybody smoked, nearly everybody with lung cancer also smoked: which is precisely what would be expected. Just as if nearly all the patients in the London Hospitals study were Londoners, it would be expected that nearly all the lung cancer patients would be Londoners as well.

Looked at this way, the London Hospitals study tells us nothing. If anything, it might even be said to give smoking a clean bill of health.

Nevertheless, when Doll and Hill commenced their next study, the much more well known British Doctors study, the focus was entirely upon smoking. The doctors were only asked about their smoking habits, and about nothing else at all. . . .

No comments: