MichaelW

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.

chasm54

Interesting to see this in the commuting forum. Say your daily commute is 30 minutes each way. You gain 2 microlifes with the outward journey, and maybe one from the homeward leg (the benefits of exercise in life expectancy tail off after the first 20 minutes). Your chances of dying on the bike is probably 2 micromorts.

So it sounds like a wash, right? Wrong. The microlife benefits keep accumulating, you don't lose them from day to day. So by the end of the week you have gained 15 microlifes in life expectancy, whereas you start afresh in terms of micromort risk every time you ride - it's still only 2 micromorts every time, because each time you survive the micromort clock is set to zero again. An interesting way of looking at how the benefits of cycling outweigh the risks - the benefits accumulate.

slowride454

hmmm I think I feel a spreadsheet coming on....

acidfast7

Personally, I think it's an excellent way to explain a probabilistic function to a layperson.

However, it is important to remember that each event is independent and not cumulative.

fietsbob

I was imagining this as coming from a microbe's perspective..

chasm54

No, not always. That is true of the micromorts - they represent the probability of an acute event - death - and they are independent rather than cumulative, the clock is reset every time you survive. But the microlife is a measure of how much an activity will lengthen or shorten your life, and that is cumulative. Repeated exercise will accumulate more microlifes, repeated cigarettes will accumulate a reduction in microlifes.