Fear is not based on what is likely to happen; it arises out of what one would not like to happen. The possibility is what counts, not the probability. The individual who is afraid of flying wants a crash to be impossible, which impossibility can only be realised by not going on a plane in the first place. The probability is of no reassurance. The converse, unfortunately, is also often true. Some people are only deterred by a probability of one hundred per cent. It takes a heart attack or actual evidence of cancer - like coughing up blood - to make some smokers give up the habit.

To some extent these "unreasonable" attitudes are understandable - and even desirable, since a life dedicated to a search for minimum risk is a boring life indeed. Most pleasurable activities carry a statistical risk, and in fact, it is arguable that the pleasure is often contingent on the risk. How then is a physician assessing the eating, drinking, smoking, sexual, or other behaviour of a patient, to decide whether he is dealing with a pleasure that is, in the patient's view, worth the risk, or a compulsion that is unrelated to any perception of risk? It is an important distinction to make, for the difference between the two is the essential difference between "healthy" and "unhealthy" behaviour.

And then there is behaviour that is not only unhealthy in its disregard for the risks involved, but irresponsible and reprehensible - like speeding under the influence of alcohol. In this case it is not just personal health that is at stake, but the health of other persons as well.

However, the most difficult questions are: who is to decide when a pleasure is worth the risk, or is compulsive or irresponsible, and what is the appropriate response? "Friends," we are told on TV, "don't let friends drink and drive". Certainly the car keys should be taken from a friend who is obviously drunk, but most alcohol-related accidents are caused by people who have only had a few drinks too many. When are friends, who are themselves drinking, supposed to say something - and risk causing offence?

Even more difficult: when are people who are not directly involved supposed to intervene? Is a doctor seeing a malignant-looking mole on a stranger's neck supposed to say anything to him? Is the health of public figures, bearing as it does on the quality of their service, to be discussed in the media? There is a particular lady, for example, whose musical talents are undoubtedly a major national resource. Having already had bypass surgery (as announced in the press), she is unquestionably eating herself into a very early grave. Is that any of our business? Those ever popular fat ladies who star on screen and stage will almost certainly die in their sixties if not before. What are their fans' responsibilities, if any? Even in such extreme cases where probabilities run close to one hundred per cent, one is likely to be accused of being "fast and out of place" for raising the issue, and not surprisingly, most people prefer to say and do nothing.

These conundrums arise when an assessment of risk is used as a predictor of events. In most cases, it is not meant to be. Risk factors are supposed to guide policy making for large groups of people. When an insurance company turns down an individual's application because he or she has diabetes, the policy makers are not saying that that particular individual is going to have a short life, but responding to the reality that diabetics on the whole have shorter lives than non-diabetics. The immediate reason for this is the diabetes, but the person with diabetes has much more to deal with than diabetes alone, and it is up to him to decide what his real risks will be.

Herein lies the important difference between a reactive and a proactive approach to health and safety. The reactive types have now built a shooting gallery where people can learn how to kill people in a cynical response to the fear of criminals that is pervading the society. Statistically, a person who buys a gun is increasing the chances that he or his loved ones will be killed or injured by a gun, whether in a domestic dispute , an accident, or in a confrontation with criminals (and, furthermore, the more people there are who own guns, the more guns there will be circulating among criminals). The reason for buying the gun, which flies in the face of the statistics, is the feeling of doing something positive, and for the Rambos who patronise the gallery, that feeling is worth the risk.

Even less rational are those people who do medical tests out of a fear of getting a heart attack. There are in fact no tests that can predict a heart attack for an individual, unless it is quite imminent. Business executives, who seem to be dropping down with heart attacks like flies these days, have all been doing "tests" for years and it has made no difference to the risks they live with. This is because a medical check up is not intended to establish - and change - a "risk profile", but to identify - and treat - disease. Where the risk is concerned, a medical check up can actually make things worse by inducing complacency.

The risk factors for heart disease are inactivity, obesity, smoking, a poor lipid profile, a family history of heart disease, high blood pressure and possibly stress. A risk profile places these factors in perspective; it indicates areas where change is needed, and if a sufficiently large proportion of the population reduces its risk, the benefits are dramatic. Americans, for example, have, in the last thirty years or so, halved the number of heart attacks that they suffer by changing lifestyle risk factors.

For the average individual, however, improved risk is little more than an academic achievement. Yes, he is less likely to get a heart attack, but the probability was not all that high in the first place. If he is mortally afraid of a heart attack, he will feel no more reassured than the person who is afraid of flying feels reassured by the relative risks of comet collisions and aeroplane crashes.

The tangible benefits of obtaining a risk profile, will, for the average individual, come from the exercise (pun intended) of reducing risk; from being proactive about his health, and from feeling healthier. He might still get a heart attack one day, but in the meantime he will look better, feel better, and enjoy his life a lot more than he would have if he had simply rested on his laurels.