Bruce Schneier

# Schneier on Security

A blog covering security and security technology.

## November 8, 2012

### Micromorts

Here's a great concept: a micromort:

Shopping for coffee you would not ask for 0.00025 tons (unless you were naturally irritating), you would ask for 250 grams. In the same way, talking about a 1/125,000 or 0.000008 risk of death associated with a hang-gliding flight is rather awkward. With that in mind. Howard coined the term "microprobability" (μp) to refer to an event with a chance of 1 in 1 million and a 1 in 1 million chance of death he calls a "micromort" (μmt). We can now describe the risk of hang-gliding as 8 micromorts and you would have to drive around 3,000km in a car before accumulating a risk of 8 μmt, which helps compare these two remote risks.

There's a related term, microlife, for things that reduce your lifespan. A microlife is 30 minutes off your life expectancy. So smoking two cigarettes has a cost of one microlife.

Snarki, child of LokiNovember 8, 2012 7:12 AM

Not to be confused with a "micro-ort", which is a barely visible scrap of food left on your plate.

kingsnakeNovember 8, 2012 7:22 AM

Sitting in traffic costs me 8 macromorts every day ...

Excellent idea. I wonder though whether it should also be per unit of time.

For the most precision it would be best to measure QALYs lost, rather than either years lost or proportion of life lost. For small measures QALH might be more appropriate - so if you have 50 quality years of life ahead of you and you go handgliding, that 8 micromort risk is equivalent to the lost of around 3.5 QALHs

lowdefinitionNovember 8, 2012 7:51 AM

There is a missing μ in the risk of driving 3000km.

bickerdykeNovember 8, 2012 7:51 AM

So.. if 1 µp is a chance of 1 to a million, please keep in mind that things that have a 1 to 1 million chance to succeed, but might happen, will work in one out of three cases...

There can't be a microlife because of micromorts. It's impossible to say how much you life has been shortened by carrying out a task. You could die tomorrow from a hang gliding accident. What should be happen is that smoking should be quantified in terms of micromorts. So smoking ten a day increases your chance of dying by say 0.01mt. You can then compare hang gliding to smoking and decide which is worth while to perform taking into account the benefits you get from them. Both are drug delivery forms, adrenaline vs. nicotine.

Alan PorterNovember 8, 2012 8:19 AM

Ah, "naturally irritating". That's the term I've been looking for. Time to update my résumé!

I really doubt that you could calculate how much longer George Burns would have lived by multiplying 15 minutes times the monumental number of cigars he smoked in his lifetime.

In this week's "what if?" by Randall Munroe (www.what-if.xkcd.com), he calculates that "a Florida resident suffers an average of 0.64 femtodeaths per second from meteorite impacts."

I'd argue that smoking a cigarette has a cost of about 0.25-0.5 microlife just from the time the smoker expends finding some place to smoke and then standing around puffing.

Clive RobinsonNovember 8, 2012 9:19 AM

It is interesting to know that your daily micromorts figure changes with age irrespective of what othe risks are in your life.

For instance (IIRC) an average healthy male aged 20 has a daily 500micromort figure, however IF the same average person makes it to 60 it has risen to 5000micromorts.

Now this gives an interesting consideration. If as a 20year old I go sky diving with say a 10micromort risk it represents a considerably higher % risk than if I was sixty...

Oh and people over say 80years of age is into serious daily micromorts of 100,000micromorts so almost anything they chose to do will have a negligable effect on their life expectancy...

@ Alan Porter

Ah, "naturally irritating". That's the term I've been looking for. Time to update my résumé

Where are you expectations?

Me I can be "super-naturally irritating" as part of the generalised theory of "one-upmanship". If some doppy g1t trying to be a smart Alex asked me for 0.00025 of a ton of coffee I would say "Is that a metric or imperial ton as it makes a difference of around 2240:2200 but I know where to look it up if you want the exact figure to the nearest mass of a silicon atom in a standard gravity if you wish?"[1]. However if you can quote the difference in actual numbers of silicon atoms that makes you "un-naturaly Iritating" :-)

[1] For those with a curiosity in "International Standards" (SI) and the units of measure and metrolology (not meteorology it makes a difference in wether you are talking about the weather or how you would standardise measuring the weather) you could do worse than start at, http://en.wikipedia.org/wiki/Metrology

Paul JohnsonNovember 8, 2012 9:37 AM

As Stalin might have put it: a single death is a tragedy, but a millionth of a death is a statistic.

Dirk PraetNovember 8, 2012 10:01 AM

Duplicate of February 8th 2011 on this blog, i.e. https://www.schneier.com/blog/archives/2011/02/micromorts.html .

conrad clarkNovember 8, 2012 10:29 AM

See also http://esr.ibiblio.org/?p=4683 , a proposal for the microzen, a unit of enlightenment.

echowitNovember 8, 2012 12:14 PM

So many μstats!

The microlife idea reminds me of the movie In Time.

"Living time", which can be transferred among individuals on body contact, is displayed on a clock implanted in people's forearms. When this clock reaches zero, one dies instantly... The poor...must work each day to earn a few more hours of life, which they must also use to pay for everyday necessities, since time has replaced money as currency.

Dr. I. Needtob AtheNovember 8, 2012 2:14 PM

It surprised me that general anesthetic is as risky as scuba diving. I wonder how that compares to the risk of not getting a colonoscopy, which includes general anesthetic. A more complete list of various activities and their associated risks could be very useful for making rational decisions like this.

Bob RobertsNovember 8, 2012 3:51 PM

“Scientists have calculated that the chances of something so patently absurd actually existing are millions to one.

But magicians have calculated that million-to-one chances crop up nine times out of ten.”
― Terry Pratchett, Mort

Terry ClothNovember 8, 2012 3:51 PM

@Clive Robinson:

At which time the Alex will reply ``Why do you say mass? It's constant (if Einstein is right) regardless of gravity. Surely you mean weight?''

@paul

http://what-if.xkcd.com/19/

In UK (in my experience), colonoscopies are performed under (optional) sedation, not general anaesthetic.

Clive RobinsonNovember 9, 2012 12:46 AM

@ Terry Cloth,

If the Smart Alex said,

`Why do you say mass? It's constant (if Einstein is right say mass? Surely you mean weight?'

He would be right about Einstein but wrong about the way we measure things...

The idea behind our current thinking on standards is to come up with just one or two fundementaly agreed methods such as counting and measuring a length. These are derived from logic via mathmatics for the likes of counting. However you end up with a problem of ratios and what your agreed standard is for "1 unit of measure" so you need primary standards that can converted to others by what are currently belived to be universal constants such as the speed of light.

But there is an issue of scale with the primary method of counting... You have to be able to have things being "singular" and "visable" to count them both of which generaly don't apply to atoms (even though the origins of the word from Greek would haave you thinking otherwise).

So with an agreement on time for which natural (almost) Universaly visable objects are good to 1 part in 10^14 stability wise, you can measure frequency (so many cycles per second) as this is related to Wavelength in a vacuum and relatavistic effects of gravity we can calculate a length by time.

Now how do we take length to mass? when you cannot count atoms, well we do it via volume and density but all substances are compressable (even the stuff in black holes) it depends on gravity...

As the irritating advert (in the UK for insurance) with the meercat says "Simpeellss".

Jon EliotNovember 9, 2012 1:56 AM

@Craig "I really doubt that you could calculate how much longer George Burns would have lived by multiplying 15 minutes times the monumental number of cigars he smoked in his lifetime."

Given the relation between probabilities in a large population and outcomes for a single individual, this might be your most well-founded doubt ever.

Dave MarcusNovember 9, 2012 8:50 AM

You would ask for 227 or 254 grams of coffee, actually. (I would ask for a short Americano, though.)

Geek ProphetNovember 10, 2012 7:54 PM

1. Microlife is a measure of life *expectancy*, not a measure of how long you will actually live. It no more tries to measure when you will die than saying that the average life expectancy of a man in the US is 75 means that all men in the US are expected to live until 75 and then drop dead.

This may not tell how long *you* will live, but this is very useful when calculating mortality rates for everything from medicine to life insurance.

2. You cannot use micromorts in this fashion. It is not clear from the article, but micromorts are a measure of the probability of *immediate* death. Since your risk of dying *immediately* from smoking a cigarette is very low, micromorts would tell you that smoking is very safe. Microlifes, however, can tell you the average life expectancy of people who have smoked X number of cigarettes and thus calculate *on the average* how much shorter their lives were because of their smoking compared to those who did not smoke. Individuals would live longer or shorter than that for a variety of reasons.

If I were to devise a poison with a 100% fatality rate, but it took exactly 10 years to take effect, and would do nothing until then, a micromort would declare the poison harmless. A microlife, however, could be used to tell you how much life life a group of people who took the poison would lose *on the average*.

@ Craig

Of course you can't determine how long George Burns would live based upon these figures. These are averages, not measures that apply to individuals. It no more tells you when a particular person will die than the odds on a roulette wheel tell you who will win.

I have several problems with this:

1. The examples suggest that it is defined in terms of 1 millionth of the subject's residual life expectancy, not total. This produces confusing and counter-intuitive results when addressed to older people. For example, for many types of risk exposures, an exposure at 22 years causes several times greater reduction in mean life expectancy than an identical exposure does at 80. (This is the case for cigarettes.) However if it reduces the life expectancy of the 22 year old by 1½ hours, and that of an 80 year old by ½ hour, these would be quoted as 3 umt and 7½ umt, incorrectly making it sound much more dangerous for the older person.

2. Some of the claims for actual values are nonsense. For example, for cigarettes Prof. Spiegelhalter ... [makes] the simplifying assumption that each cigarette contributes equally to the risk. This is not simplifiction, it is wrong. There does not exist a simple linear relationship between number of cigarettes consumed and reduced life expectancy. This isn't to say that people shouldn't be warned that it is very unwise to smoke and a good idea to quit; but it is false to say that "each cigarette loses 15 minutes of your life", and stating falsehoods doesn't help the argument.

3. The one for BMI is even worse. To force it into this proportionality model, he ignores several key features of the paper he cites. In particular, he grinds his microlife values out of a reported hazard ratio using a calculation based on Gompertz' appromximation; all the while missing that the cited article's figures (especially Fig.7) give the result directly. Those figures, however, would have been a little unsatisfactory: they show that i) the relationship is not remotely linear; ii) for BMI ranges below 22, it is negative i.e. losing weight shortens life expectancy; and iii) most importantly, for BMI below 35 (the supposed boundary between "moderately obese" and "severely obese"), the relationship is weak with both a small slope and weak correlation; nearly all the upswing is actually in the severely obese zone. To characterise this as "each 5 kg of overweight reduces life expectancy by 1 umt" is a completely false representation of the results in the cited paper.

4. Presumably this sentence is a typo: "This means he is losing around 350 days life-expectancy, 16,500 microlives, for every day he is overweight." (If that was the case he would be dead in two months.)

5. But my worst gripe by far: The real problem -- and a perennial problem in many epidemiological studies -- is that there is large uncertainty in the results and it is rarely reported to the public nor to policy makers. In this BMI data, the 95% confidence intervals for the two BMI zones used by Prof. Spiegelhalter actually overlap by around 60%. Based on this data, we cannot state with confidence that a 1.75 m tall man who lowers his mass from 78 to 73 kg will thereby probably live 350 days longer. On the contrary, we do not even have very high confidence that he will increase his life expectancy at all; in fact there's even about a 10% chance that losing weight will actually lower his life expectancy. This is one of the a perennial bug-bears of epidemiology: results are published at very low confidence levels, or with confidence intervals that overlap "no effect", or without even calculating confidences; and are then made to seem important by multiplying a large "exposed" population by a highly uncertain number that is close to zero and may in fact be zero. The result is that people have learned to ignore epidemiological Cassandras not because they do not understand risk; but because they are fed up with an endless series of contradictory proclamations that are rarely substantiated.

6. JonathanNovember 19, 2012 5:33 AM

The concept is great, the terminology deplorable. "Micromort" is a mangle of Greek prefix and Latin root.

What's wrong with "microthanatos"?

"Microlife" is even worse, since it uses an English root -- hardly appropriate for an international scientific concept. "Microbios" would work far better.

Mr MetricNovember 19, 2012 11:22 AM

Somehow I would imagine that asking for anything in metric when shopping in the states would instantly label you as "naturally irritating" ...

Half a pound of coffee, surely.

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