No pleasure is worth giving up for the sake of two more years in a geriatric home at Weston-super-Mare. Kingsley Amis
A constant theme in this blog has been how we tend to misjudge risk. After a terrorist incident many people change their mode of transport from plane to car or from bus to bicycle, even though the new ways are much riskier. We hear a lot about drink driving, but what about drink walking? When I write about these topics, I tend to use the pronoun we. I am not immune to these errors.
Comparing and communicating these small but lethal risks is a complicated task, but there is a handy tool available to help us in this endeavour – the micromort. We have Ronald A. Howard, a professor at StanfordUniversity, to thank for this extremely useful concept. An expert in decision analysis, he wanted to break down the idea of fatal risk into small units. Mr. Howard will be eighty this August, so he does seem to know something about staying alive.
The micromort, which represents a one-in-a-million chance of death, enables us to us to convert small risks into whole numbers that can be easily compared. David Spiegelhalter explains it very well in the video above: If you threw 20 coins in the air, the likelihood that they’d all come down heads would equal roughly one micromort. Spiegelhalter illustrates it simply. Typically, about 50 people in England and Wales die accidentally or violently each day by what are known as external causes. As there are roughly 50 million people in England and Wales, this means that about one in a million shuffle off this mortal coil in this way, every day. So this daily risk for the population of England and Wales is in the region of one micromort. This is the risk of an average citizen. But of course we are not all the same. Some of us are extremely risk-averse, whereas others think nothing of jumping off a mountain. There are some interesting statistics in the video here are a few more I found on Wikipedia:
Hang gliding – 8 micromorts per trip
Scuba diving – 4.72 micromorts per dive
Skydiving (in the US) – 7 micromorts per jump
Horse-riding – 0.5 micromorts
Ecstasy (MDMA) < 0.5 micromorts
The comparison between ecstasy and horse riding is what got David Nutt the Labour government’s scientific adviser sacked, another victim of the crazy war on drugs.
Age also comes into play too. I heard these statistics in a video on the Mental Floss website: A 59-year old man has an overall risk of 7,000 micromorts, which means a 7% chance of dying. By the age of 85, this will have reached 200,000 micromorts, or a 20% risk of death.
However, there are many other risks we take don’t kill us straight away. These are lifestyle choices such as smoking, drinking, eating badly, not doing exercise and so on. Spiegelhalter has come up with a new measure to deal with these risks- the microlife. This aims to make all these chronic risks comparable by showing how much life we lose on average when we’re exposed to them; a microlife is 30 minutes of your life expectancy.
Here are some things that would, on average, cost a 30-year-old man 1 microlife:
Smoking 2 cigarettes
Drinking 7 units of alcohol (e.g. 2 pints of strong beer)
Each day of being 5 Kg overweight
You can also gain microlives. 20 minutes on any given day exercising vigorously will “earn” you two microlives – an extra hour’s breathing. Alas, there are diminishing returns; every extra 40 minutes exercising after that buys only 30 minutes.
Micromorts and microlives measure different kinds of risk. If you survive your motorbike ride, then your micromort slate is wiped clean and you start the next day with an empty account. But if you smoke a pack of cigarettes a day, drink 10 beers and live off fast food, then your microlives will accumulate. Spiegelhalter compares it to a lottery where the tickets you buy each day remain valid for ever – so your chances of “winning” increase every day.
Are these measures useful? I think they are. Some argue that these numbers are only useful to insurance companies and governments and they tell you nothing whatsoever about whether any individual will actually be harmed by the particular behaviour, because there are always people who engage in the behaviour in question and do not suffer from it. Moreover, they may give more ammunition to scaremongers – fuelling paranoia like those tabloid news stories. Nothing can guarantee that we will live to one hundred. But I think it is always better to be informed. I don’t think it need make us neurotic. We all need to know our risk profile. Mine happens to be quite low. But if you have high risk tolerance, go ahead and do what turns you on.
Linguistic note: I couldn’t find a precise etymology for micromort. There is also an alternative spelling – MicroMort. In different pieces I have seen Spiegelhalter spelling it both ways. And as I am typing this post Microsoft Word underlines the word in red every time I write it. It is a pity that a word whose origins lie in the 1970s has not achieved greater recognition.