Nothing short of proof

Saturday's fortnightly column is for tenuous links between archival material and something contemporary.

In the early 1960s, it was popularly believed that blood group affected one's susceptibility to various diseases. In 1962, Alexander S. Wiener criticised the supposed link between blood group O and duodenal ulcer, showing that the data used to support the hypothesis was faulty. Wiener was in turn criticised for providing no empirical data of his own: he may criticise the data used to support the hypothesis, but he has provided no data to support the alternative – that there is no link. He replied:

This is not necessary, since it has been possible to demonstrate that the data already accumulated, on which the claims are based, are faulty. Moreover, it is not necessary to practice chiropracty in order to demonstrate that chiropracty is a form of quackery: nor is it necessary to try out every crack-brain claim in order to prove such ideas to be fallacious.^[1]

It took a further two decades for the blood-ulcer link to finally die out. It's hard to kill a bad idea once it has spread far and wide. I picked the blood-ulcer link because of the quote, but the history of medicine is littered with examples that I could have chosen. Some of them are blatant quackery, but many are simply mistakes: too much confidence in or extrapolation of faulty but not fraudulent data. Once one has accepted that an idea is true, one often has difficulty rejecting the idea when the original argument that convinced you of its truth is shown to be unsound. When the supporting evidence is removed, instead of accepting that Ockham's Razor (the law of parsimony) rules against one's idea, one is tempted to believe that, in the absence of evidence either way, one can give equal weight to the positions that one's pet idea is true or false. This is an example of what psychologists call “cognitive dissonance.”

In medicine, doctors are often guilty of keeping alive hypotheses that have no right to their protection. But at least as often, the media and lobby groups are responsible. For a decade, the media – and not just the usual suspects in the tabloids – have propped up one such hypothesis: the MMR-autism link.^[2] The link was made on the back of genuine research, but this was later shown to have methodological problems, and is now agreed to be unreliable. Further studies attempting to replicate those results failed to find any such link. Scientists therefore dismissed the hypothesis with Ockham's Razor. The media, however, merely relegated the MMR-autism link to a position which has equal weight with the opposing position – that there is no link. Now campaign groups tell us that those who deny the link are acting unscientifically by not collecting more data. Not content with a lack of any reason to believe that such a link exists, they demand strong evidence that no link exists before they will give up on it.

Sometimes advocacy groups of this sort will point out that, unlike in the blood-ulcer example, when it comes to the introduction of new synthetic chemicals and technologies, the burden of proof is upon those introducing these potential new hazards to prove that they are within standards of safety. One might think that this is the case, for example, with last week's announcement by the British government that it would fund further research into the safety of wi-fi. But in neither the MMR or the wi-fi cases are these organisations campaigning on a platform of general concern for safety. The MMR campaigners want research that confirms their belief in a link specifically to autism, and the wi-fi campaigners have their own set of conclusions that they want vindicating. The organisations are not campaigning for analyses that look for all potential health consequences of these technologies, they are concerned only with research into their pet hypotheses. If these campaigners truly are concerned primarily with holding pharmaceutical and electronics companies responsible, why devote so much time to single hypotheses about single technologies, and so little time to general regulatory laws and protocols?

 

References

1. ^  Quoted in Skrabanek and McCormick, 1990. Follies and Fallacies in Medicine. Prometheus.
2. ^  Goldacre, B. 2007. Medicine and the media: MMR: the scare stories are back. BMJ. 2007 Jul 21;335(7611):126-7