Understanding probabilities is hard (viz.) — and it’s especially so when we try to understand and take rational decisions based on very small probabilities, such as one-in-a million chance events. How, then, to communicate risks on a similar level, too?

The answer is to use a more understandable scale, such as micromorts; “a unit of risk measuring a one-in-a-million probability of death”. Some activities that increase your risk of death by one micromort (according to, among other sources, the Wikipedia entry):

• smoking 1.4 cigarettes (cancer, heart disease)
• drinking 0.5 liter of wine (cirrhosis of the liver)
• living 2 days in New York or Boston (air pollution)
• living 2 months in Denver (cancer from cosmic radiation)
• living 2 months with a smoker (cancer, heart disease)
• living 150 years within 20 miles of a nuclear power plant (cancer from radiation)
• drinking Miami water for 1 year (cancer from chloroform)
• eating 100 charcoal-broiled steaks (cancer from benzopyrene)
• eating 40 tablespoons of peanut butter (liver cancer from Aflatoxin B)
• eating 1000 bananas, (cancer from radioactive 1 kBED of Potassium-40)
• travelling 6 miles (10 km) by motorbike (accident)
• travelling 16 miles (26 km) on foot (accident)
• travelling 20 miles (32 km) by bike (accident)
• travelling 230 miles (370 km) by car (accident)
• travelling 6000 miles (9656 km) by train (accident)
• flying 1000 miles (1609 km) by jet (accident)
• flying 6000 miles (9656 km) by jet (cancer from cosmic radiation)
• taking 1 ecstasy tablet

Issue fifty-five of Plus magazine looked at micromorts in more detail, thanks to David Spiegelhalter (the Winton Professor of the Public Understanding of Risk at the University of Cambridge) and Mike Pearson, both of Understanding Uncertainty.