Of war and peace
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understandinguncertainty.org was produced by the Winton programme for the public understanding of risk based in the Statistical Laboratory in the University of Cambridge. The aim was to help improve the way that uncertainty and risk are discussed in society, and show how probability and statistics can be both useful and entertaining.
Many of the animations were produced using Flash and will no longer work.
DJS, Times Eureka blog, 14th June 2010
Comparing different risks can be a risky business. Professor David Nutt found this when he weighed the harms of ecstasy against ‘equasy’, the addiction to horse-riding, and found they were broadly comparable.
Even though both are voluntary activities conducted mainly by young people for fun at weekends, the angry expostulations that followed suggested he had broken a cultural taboo in objectively comparing ‘wholesome’ approved behaviour with illegal acts. But the comparison was still illuminating.
I gave a talk on risk at the Cheltenham Science Festival on Saturday in which, with some trepidation, I made a similarly delicate comparison: who is exposed to the greater lethal risk - a member of the UK forces serving in Afghanistan, or an average patient spending the night in an English hospital? Of course the question can’t be answered exactly: it all depends on who we mean and how we measure risk. But statistics can give us a ball-park figure that may be surprising.
Let’s take Afghanistan first. Tragically, as reported by Bird and Fareweather, UK forces suffered 44 deaths in the 20 week period up to 21st February, with around 9,500 personnel serving each day. A 1-in-a-million chance of death is known as a micromort, and so that’s an average of 33 micromorts every day for every serviceman and woman – that’s around the risk of a motorbike ride from London to Manchester. Of course the word ‘average’ is crucial as front-line troops were exposed to considerably greater risk than this. They fully deserve our respect, as do the US forces, who were each exposed to a daily average of 11 micromorts over the same period.
But what about going into hospital? Each day in England around 135,000 people occupy a hospital bed and inevitably some of these die of their illness. But not all these deaths are unavoidable: in the year up to June 2009, 3735 deaths due to lapses in safety were reported to the National Patient Safety Agency, and the true number is suspected to be substantially higher. This is about 10 a day, which means an average risk of around 1 in 14,000, assuming few of these avoidable deaths happened to out-patients.
So staying in hospital for a day exposes people, on average, to at least 70 micromorts. This is equivalent to the average risk of riding 420 miles on a motorbike, say between London and Edinburgh. The conclusion: hospitals are high-risk places.
This comparison should not in any way downplay the risks being faced by UK troops, and it would be ridiculous and insensitive to say that staying in hospital is twice as dangerous as serving in Afghanistan. Nobody chooses between the two options - these are different people in very contrasting circumstances, and averages only provide a rough assessment of the risks faced by an individual.
But getting an idea of the size of the lethal risks faced by different groups of people can be illuminating particularly when, as in the ecstasy/equasy comparison, one cause of death gets substantial publicity. Any avoidable death is a cause for sadness and regret.
