risk analysis: micromort and microlife
Just been listening to an interview on radio with a statistician who talked about 2 concepts useful for analysing risk: the micromort and the microlife.
Micromorts are a unit of risk measuring a one-in-a-million probability of death. You can say that a mode of transport results in so many miles per micromort and the result is a number you can really use. For cycling, this is 10-20 miles, for driving it is about 230 miles.
Microlifes are a millionth of an (average remaining) lifespan = 30mins of life, so activities which extend your life or decrease it in a chronic rather than acute way can be measured.
In looking at the risk associated with cycling to work, people often quote the mort factor You also have to include the life factor. First 20mins of excercise = +2 microlifes . Sedentary behaviour = -1 microlife
This kind of calculation is really more suited to examining the effect of activities on populations rather than individuals. It may seem odd to put such precise numbers onto activities but the people who make decisions abut transportations, planning etc only account for numerical factors, eg the time saved for drivers.