Living beyond your genes

Paul Slade explains how reports of the death of actuaries' tables have been somewhat exaggerated

A new science fiction film, Gattaca, shows a society where genetic testing can determine people's lifespan at birth. In real life, insurers don't find things quite that simple.

Although DNA testing may play a part in life insurance underwriting soon, insurers have so far relied on tables of past mortality statistics to control the risk they accept.

Making DNA testing a part of underwriting would create a whole web of moral problems. High-risk groups already pay a higher premium for their life and health cover under the existing system. Some fear genetic testing would take this a huge step forward, allowing insurers to refuse applications from anyone whose DNA suggests they are at high risk of serious disease.

In any event, there are limits to what DNA sampling alone could tell insurers - no matter how sophisticated the technology may become.

Paul Greenwood, research actuary at William M Mercer, says: "You'd still have some statistical averages coming into it. What you don't know, looking two or three years ahead, is how harsh the winter is going to be, which still seems to have an effect [on mortality]. You also don't know whether the long-term improvement in mortality is going to speed up or slow down."

Nigel Masters, a partner at Coopers & Lybrand, sounds a similar note of caution. He says: "Within the actuarial profession, there's considerable debate over whether DNA testing is going to be of any great use at all."

The closest actuaries can come to forecasting a particular individual's age at death is to calculate the age at which his or her chance of still being alive is 50/50. For a man aged 30, this would be the age at which statistics suggest only half of today's 30-year-old men will still be alive. The first table shows where this age falls for various age groups.

For actuaries, the single biggest determinant of when you are going to die is when your parents died. But this only indicates that you will share some of the same risk factors as your parents. The actual outcome in your own case may be very different.

Mr Masters says: "Your family may have weak hearts but, if you keep fit and don't eat any fatty foods, that may never be a problem for you. If your father died of lung cancer, but you don't smoke, you're probably OK."

All actuaries like him can do is took at large groups of roughly comparable people and say what the average age of death for that group might be. Any real death in the group may fall 30 years or more after the average. But the fact that people your age can, on average, hope for another 40 years will not help you if you fall under a bus tomorrow.

The good news is that, the longer you live, the longer you can expect to go on living. For example, figures from the Government Actuary show that a man of 40 can expect to live for another 35.96 years. Assuming he survives to 45, he can then look forward to another 31.31 years.

In other words, he has lived for a full five years, but reduced his future life expectancy by only 4.65 years - a "profit" of 128 days. This effect continues throughout life. Even the average 105-year-old, simply by virtue of having made it that far, can expect to enjoy two more birthdays.