Robert May: Trust me, I'm a scientist

Yet another study was published this week showing a lack of evidence for homeopathic remedies having anything more than a placebo effect. It was the latest in a long line of studies over the past 150 years demonstrating not only that homeopathy has no intrinsic benefit, but also that there is no plausible physical mechanism through which extremely diluted solutions could act therapeutically.

But even though objective scientific studies deliver the same verdict about homeopathy time after time, they will continue to be disregarded by a sizeable proportion of the population, including many doctors, who maintain the belief that homeopathy works. It is yet another example of some people - a large minority - not believing the evidence presented by scientists.

Such disregard for evidence, of course, is not new. Indeed it was only four centuries ago that a group of scholars founded the Royal Society to promote the radical notion that our understanding of ourselves and the world around us should be based on experiment and observation, rather than merely speculating about things. This revolutionary approach was so successful that it not only provided the fundamental basis for how all science is carried out today, but was a key factor in the rise of the Enlightenment movement, as outlined in John Gribbin's new book The Fellowship, published this week.

Even though the value of the scientific method is now well established, it is perhaps surprising that the Royal Society's motto, Nullius in verba, or roughly "trust not in words alone", remains as relevant today as it did in 1660. There are still those who are not interested in what the evidence shows, preferring instead dogma or belief.

Although there is a lot of evidence that homeopathy has no intrinsic beneficial properties that cannot be attributed to the placebo effect, this does not mean it is completely impossible that one day additional benefits may be found. This lack of absolute certainty is a feature of almost all areas of science, and can often be the source of confusion and controversy, within and outside the research community. It presents politicians with the difficult problem of how to make wise policy in such circumstances.

Take the recent controversy over the MMR vaccination. Numerous studies have shown the value of the jab in protecting children against the three serious, and sometimes fatal, diseases. But no vaccination can be asserted to be 100 per cent safe. There may always be individuals, albeit a very small minority, who could suffer an adverse reaction. In the case of MMR, however, these costs - if they exist at all (and there is no evidence that they do) - are clearly very much smaller than the protective benefits conferred by the triple jab.

When it was claimed in 1998 by Andrew Wakefield that there was evidence of a link between MMR, autism and bowel disorders, the UK Government rushed to assure parents of the safety of the jab. But the campaign to restore public confidence was undermined by well-meaning and unequivocal assertions of absolute safety. It was clear that MMR was not responsible for the ill effects suggested by Dr Wakefield, but it just was not possible to say that no child would ever suffer any adverse reaction. Attempts to provide excessively absolute assurances had the opposite effect on some people, particularly in the aftermath of the BSE controversy, causing them to lose confidence in the official advice they were receiving.

What would have been better would have been an open admission that there theoretically might be very small risks for some children (although not more than 1 in 100,000), and an explanation of how mass vaccinations expose individuals to such risks in order to protect the population as a whole from the far greater risks posed by serious diseases.

Of course, it is easy to be wise after the event. The task of providing the public with the information they required was made much harder by some elements of the media which decided to campaign on the issue, falsely giving the impression that a conspiracy within the medical profession was hiding the true story about the safety of the jab.

Those newspapers that campaigned against the MMR jab were at least partly responsible for making a proportion of the population wrongly believe that many researchers, rather than one or two individuals, thought that the vaccination posed a major risk. And there are those who still cling to the belief, even in the face of yet more evidence of the jab's safety, that there is a serious health threat.

One of the central features of the MMR controversy was the question of uncertainty. Was it possible to be certain that any particular child might not suffer some sort of ill health from the jab?

The answer was no, but some wrongly interpreted this to mean that a wide range of possibilities could exist, such as a large threat to many children. In fact the correct response would have been to openly acknowledge and quantify any uncertainties and to make wise policy accordingly.

This of course is a key element of the so-called precautionary principle. Although most policy-making implicitly operates according to this principle, some people and organisations advocate an extreme interpretation of it. They argue that nothing new should be introduced unless it can be proven absolutely in advance that there will not be some sort of adverse effect on human health or the environment. Such an approach is a formula for bringing progress to a grinding halt and for forgoing any future benefits from advances in our knowledge.

The precautionary principle is best applied in commonsense terms. Assess the possible risks and benefits from the evidence that you have, and do not do anything that you think will have more adverse than beneficial effects. This does not mean that all problems will be avoided, since some are unforeseeable, but it is the basis of sound decisions.

One of the reasons why this apparently sensible approach can be so controversial is that many people are not comfortable with the concept of uncertainty in science. At school, most science lessons concentrate on the learning of facts and figures, a set of certain answers to clearly defined questions. This is not how science proceeds, particularly at its frontiers where new knowledge is being acquired.

It would be much better if school science lessons offered a better reflection of how science actually advances, and gave a sense of the scientific method. To make pupils aware of what we do not know as well as what we do know. To show how scientific knowledge grows through a never-ending quest for a better understanding, providing us with more certainties in some areas, and more uncertainties in others.

It is therefore reassuring that the slimmed-down GCSE curriculum from next year will focus more sharply on the learning of the scientific method. This will hopefully better equip future generations to grapple more effectively with the scientific controversies that they face, and allow them to be better placed to recognise whether the purported benefits and risks of new medicines or technologies are supported by hard evidence or just empty claims.

Lord May of Oxford is president of the Royal Society, the UK national academy of science