Nornagest comments on How to avoid dying in a car crash - Less Wrong

75 Post author: michaelcurzi 17 March 2012 07:44PM

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Comment author: bentarm 20 March 2012 04:56:58PM *  30 points [-]

I think this post could do with some estimates of absolute risks.

According to the site you link to, there are 7476 deaths in traffic accidents for people in the 15-24 age range (NB - this presumably includes pedestrians, so is a massive overestimate of the deaths of people who were driving, but I'll go with it for now).

In total, there were 21,859,806 males in your age group, so your probability of dying in a road traffic accident in any given year is approximately 0.0003. This translates to a risk per day of approximately 0.0000009.

Combining these numbers naively, the risk of being involved in a traffic accident on the first snowy day is approximately 0.0000009*1.14. In other words, your excess risk of dying by driving on the first snowy day is approximately 0.0000001. Even assuming that driving in snow is 10 times more dangerous than driving in normal conditions, this risk is 1 in 1 million. Is it really worth going out of your way to avoid driving on the first snowy day to avoid a 1 in 1 million increased chance of dying?

It is worth noting that as an avid transhumanist, I might well expect Michael to think that a 1 in 1 million increased chance of living as long as the Singularity, or dying in such a way as to allow his head to be frozen is probably worth quite a lot. But by revealed preference, most people in the US are only willing to pay around $10 to avoid a 1 in 1 million chance of dying (cf The Value of Statistcal Life), and so should probably only avoid driving on the first snowy day if they'd be willing to pay less than $10 to avoid the inconvenience.

The other examples could do with a similar analysis. A good way of thinking about it is how many fewer people would you expect to die if 1000 people took your advice.

Another point is that, even for the avid transhumanist, it seems unlikely that avoiding traffic accidents really is the best way of trying to live long enough to reach the Singularity - basically no-one dies before the age of 40 - a much more common cause of death among today's 15-24 year olds than dying in an RTA is living until you're 45 and then dying of Coronary Heart Disease, so you should probably look at optimising your lifestyle/diet to avoid that before you worry too much about getting an ipod cable for the car (although, actually, just running some quick numbers in my head, it seems like that one is likely to be a good investment). I note Dymtry has already made a comment along these lines.

Finally, some of the advice from other people that you've included in your bullet-pointed list is just terrible. Cycling is around 10 times more dangerous per passenger mile than driving. One anecdote which says that cycling might increase your ability to drive safely cannot possibly outweigh the massive evidence that says cycling is massively more likely to get you killed than driving is. Similarly, I would like to see some evidence that, say, driving safety courses actually help. Someone on the internet said so is not very convincing.

What's my point?

First - thou shalt not report odds ratios. There is a wealth of literature on the subject which says that people make better decisions when present with absolute risk estimates than with odds ratios.

Second - it always pays to crunch some numbers. Car crashes are the most common cause of death among 15-24 year olds, but it is far from clear that steps taken to avoid car crashes are the best way for 15-24 year olds to extend their lifespan.

Third, [citation needed]. If you are compiling a list of advice like this, I think the onus is on you to make some effort to check that the advice you're giving is useful, or at least to put a disclaimer saying that you haven't. This could be useful resource, if it could be trusted.

Comment author: Nornagest 20 March 2012 06:12:47PM *  2 points [-]

this presumably includes pedestrians, so is a massive overestimate of the deaths of people who were driving, but I'll go with it for now

This page claims that pedestrian fatalities represent about 11% of the total fatalities from motor vehicle accidents, so it's in the same ballpark either way. I wouldn't call that a particularly authoritative source, but by some back-of-the-envelope math it's fairly consistent with your numbers.

Comment author: bentarm 20 March 2012 06:34:58PM 2 points [-]

Thanks for checking. I probably should have bothered to do that myself, after berating Michael's lack of scholarship. This UK government publication says that 25% of road deaths were pedestrians, and 50% were car drivers, so yes, figures for total casualties are basically the same as figures for car drivers.