The Micromort & Microlife

Number geeks should check out Understanding Uncertainty.  For those of a paleo bent, a good starting place is "What does a 13% increased risk of death mean?" which looks at red-meat consumption and death rates.  It is all a bit technical in places, but persevere with it and it is rather informative (I also recommend DC's Improbable Science and this post on the same topic).

The website makes much of the micromort (a unit of risk measuring a one-in-a-million probability of immediate death) and the microlife (30 minutes of your life expectancy),

• "...many risks we take don’t kill you straight away: think of all the lifestyle frailties we get warned about, such as smoking, drinking, eating badly, not exercising and so on. The microlife aims to make all these chronic risks comparable by showing how much life we lose on average when we’re exposed to them."

The microlife was formulated by David Spiegelhalter and he explains its relationship to the micromort thus,

• If we expose ourselves to a micromort, we take a 1-in-a-million chance that our future life will be 0, and hence our life expectancy is reduced by a millionth. Hence a young adult taking a micromort’s acute risk is almost exactly exposing themselves to a microlife. An older person taking the same risk, while still reducing their life-expectancy by a millionth, is only perhaps losing 15 minutes life-expectancy. However, acute risks from dangerous activities are not well expressed as changes in life expectancy, and so different units appear appropriate.
  
  There is one big difference between micromorts and microlives. If you survive your motorbike ride, then your micromort slate is wiped clean and you start the next day with an empty account. But if you smoke all day and live on pork pies, then your microlives accumulate. It’s like a lottery where the tickets you buy each day remain valid for ever - and so your chances of winning increase every day. Except that, in this case, you really don’t want to.

 To hear more about David Spiegelhalter check out this excellent podcast on The Life Scientific,

• Is it more reckless to eat a bacon sandwich everyday or to go skydiving? What's the chance that all children in the same family have exactly the same birthday? Jim Al-Khalili talks to Professor David Spiegelhalter about risk, uncertainty and the real odds behind everyday life.
  
  As one of the world's leading statisticians, he is regularly called upon to help answer questions in high profile inquiries - like the one into the Harold Shipman murders, infant heart surgery at Bristol Royal Infirmary and the PiP breast implant scandal.
  
  Jim finds out more about the Life Scientific of the man who despite winning many awards and his research papers being some of the most cited in his field David Spiegelhalter says he isn't really that good at maths.