We were talking at the weekend about the concept of “micromorts” and “microlives”. I had read about it sometime over the last year in the New Scientist and have just dug out that copy of the magazine. I was surprised to find that it was nearly a year ago (the 30 May 2015 edition). I imagined that it was in November or December of last year, or maybe earlier this year. Nope, nearly a whole year ago.

It was the in the Cover Story, “Getting away with it”, summarized as “Guilty Pleasures you can sometimes indulge – and ones you can’t”. It has headings like Chocolate, Inactivity, Red Meat, Booze and Flying and looks at the risks of each. What caught my eye then (and has stayed in my mind since) was the concept of Micromorts and Microlives. In a piece titled “Weighing up the risks” statistician David Spiegelhalter explains how it works. Rather than paraphrase it, I’ve copied the first three paragraphs here:

Calculating whether your guilty pleasure pays is hard: statements about health risks and benefits can be tricky to wrap your head around.

With activities like motorcycling or skydiving, one way is to think in micromorts –a micromort being a one-in-a-million chance of dying then and there. This unit is useful for pursuits that could kill you on the spot, says statistician David Spiegelhalter of the University of Cambridge. “When you do these activities, you are going to be healthy unless you are dead.”

For lifestyle choices that chip away at good health – eating to excess, or smoking – think instead in microlives. A microlife is a millionth of a life, and equates to about half an hour. Spiegelhalter reckons that, for regular smokers at least, every two cigarettes costs one microlife. “This enables you to make comparisons across broad ranges of activities using common units, and without having to use very technical units like person years lost per something, or hazard ratios,” he says.

[You can read the piece (350 words or so) in this link to a PDF on the New Scientists website (“Weighing up the risks”, at the bottom of the page).]

There is also a simple “Microlife Calculator” which lists the positive or negative effect of watching TV (sedentary), smoking, drinking alcohol and exercise.

2 hours watching TV (sedentary) is -1 (i.e. minus one microlife: it will reduce your life by 30 minutes; but if you get up and walk around for 5 minutes in every hour the negative impact will be neutralized).
As mentioned above smoking 2 cigarettes is also -1 microlife (again, it will reduce your lifespan by 30 minutes).
Your first unit of alcohol in a day, however, has a score of +1: it has a beneficial effect of 1 microlife, but that will be counteracted by each further unit of alcohol that day (each subsequent unit, up to 6, has a score of -1/2). That suggests that 3 units of alcohol would have a neutral impact overall, 2 units would have a positive impact of half a microlife, but anything over 3 units will have a negative impact.
Finally, the first 20 minutes of physical activity is worth +1 microlife (and each subsequent 40 minutes is worth a further +1 for a man or +1/2 for a woman).

I have just downloaded the Kindle edition of Spiegelhalter’s book (“The Norm Chronicles: Stories and numbers about danger”, written with Michael Blastland) but won’t look at it yet. I have already been sat at this screen for 90 minutes so it’s time to move around a bit (otherwise that’ll be a micromort, reducing my lifespan by 30 minutes). It’s possible that the most important information in the book is already summarized above, but I’ll post updates with any further nuggets from the world of micromorts and microlives, or you could read it and tell me what  you find.

UPDATE (19 May 2016)
I managed to read “The Norm Chronicles” this month and have posted this piece as a follow-up.