This has prompted suggestions that work needs to be done on risk evaluation as distinct from risk assessment - where scientists assess risks using available data. Unfortunately, resources for risk avoidance continue to be allocated more by personal perceptions, and radiation is probably the area where there are the least valid perceptions.

For example, parents can become distraught about their child needing five x-rays. Yet they would probably be entirely unconcerned by the greater radiation dose incurred during a flight to Florida, or a week in Cornwall, even if they knew anything about it.

Amongst the key factors that govern risk perception are:

1. If an activity is enjoyable or profitable, risk tends to be disregarded. Avoidable lifetime risk factors of up to 20% seem tolerable to some people.

2. If the source of the risk is natural, less concern is generated than for an equivalent man-made hazard, especially if someone can be found to take the blame.

3. Anything to do with nuclear power is assumed to be dangerous, and anything to do with disposal of nuclear waste is assumed to be doubly dangerous, despite that personal lifetime risks may be below 10-{.

4. Events that cause many deaths at once receive proportionally more publicity.

Confusion stems to some extent from mixing up environmental, health and nuclear issues, and trying to compare them one with another. Section 22 contains a more detailed discussion.

This Section presents the risk from radon within an overall cancer perspective, and using a presentation that has proven comprehensible to many homeowners. All estimates are for non-smokers, since the real magnitude of the radon problem is that remaining once smoking has been phased out.

In the UK, as in many other western countries, the average lifetime risk of dying of cancer is between 1 in 5 and 1 in 4, or between 20 and 25%. This is a greater risk than in many underdeveloped countries simply because many people there die before they have much chance of contracting cancer.

In the UK, the risk of dying from radon after living for 10 years in one of the worst-affected houses (say at 2000 Bq/m³) may be less than 2%. This severe radon exposure increases total cancer risk from (about) 20 to 22%. However, simply changing from an unhealthy to a healthy diet may well decrease overall cancer risk by 2 or even 4%. There may also be other health benefits from better diet.

However, if "living with 2,000 Bq/m³" were to be described in terms of a radiation dose 50 to 100 times as great as that received by most workers at nuclear power plants then panic might be the first reaction. The problem here would be that radon had been set in a nuclear context, rather than having been explained as one more health issue amongst many.

The sketch below shows what has become one of the most useful presentations of radon risk: the large box represents the overall risk of death at some time (100%, or an absolute certainty). The smaller boxes show the lifetime risks from given exposures to radon, all for non-smokers. Risks to heavy smokers may be more than ten times as great, but with incidence reduced by competing causes of death.

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