05:08 pm, Monday 2 April, 2012
Living is risky. When we cross the street, we risk being hit by a car. When we climb a high ladder, we risk falling from the top and dying. We are constantly reminded of how to control or eliminate risk in our lives. Eating a healthy diet, getting regular exercise, and keeping our relationships healthy are all meant to decrease our risk of an early and untimely death. We can’t eliminate 100% of the risk in our day to day life – so how can we compare the real risks we face every day and decide which ones are worth avoiding?
David Spiegelhalter, Winston Professor of the Understanding of Risk,UniversityofCambridge, provided a lesson in how risk can be measured on the BBC’s ‘Future’ site over the weekend. The article raised some questions about risks that are acute or chronic and how they might be compared to each other.
To provide a single unit of measurement, scientists at StanfordUniversitydeveloped the micromort in the 1970’s. This is the name given to a one in one million risk of dying from an unnatural cause. Our daily risk, just by being alive, is equal to 1 micromort. We can double that by flying 1600kms on a jet, walking a little over 27kms, or travelling 370kms by car. Skydiving is a little riskier with each dive worth 7 micromorts. These are all acute risks and each day we start afresh – with our existence risk rate just 1 micromort again.
Chronic risk is a little different, however. For an Australian man aged 25 in 2006, his average life expectancy would be about 79 years. A microlife represents 30 minutes of your life expectancy. So this young man could expect to have around 950 000 microlives left. If he chooses to smoke, drink heavily or be overweight, his life expectancy decreases. As an example, for each day someone is 5kg overweight, they reduce their life expectancy by 1 microlife or thirty minutes. Smoking two cigarettes or drinking three full strength stubbies will each reduce your life expectancy by 1 microlife. Unlike acute risk, microlives are cumulative. That is, they add up day after day and reduce your overall life expectancy. So, if our young man smokes 25 cigarettes per day for the rest of his life, he will reduce his life expectancy by 14 years.
Professor Spiegelhalter also studies the nature of risk taking and why some people are high risk takers and others risk averse. It might all depend on whether you want to measure your risk in micromorts or microlives.