Friday, October 12, 2007

The Odds of Your Being Killed in a Car Accident

It strikes me that there is something muddled about comparing something like "a person's odds of being killed in a car accident" with something along the lines of "that person's odds of being killed in a plane crash," noting that the first odds are lower than the second, and then concluding that anyone who is concerned about flying but routinely drives is "irrational." No doubt it is true that people frequently overestimate risk connected with some rare but attention-grabbing calamity that has just made the news, while remaining blase about the risks involved in more mundane activities.

But my complaint concerning the above situation is that the odds of being in a car accident are not really odds at all. That's because those "odds" are arrived at by treating the occurence of accidents as purely random events that simply "happen" to drivers, like being struck by a meteor. To the contrary, any individual driver's likelihood of having a collision is affected quite significantly by how she drives -- her skill, her knowledge of her car, her degree of focus, and how much caution she exercises. For instance, one can only collide with another car after first closely approaching it. (Automobiles have not been observed making quantum jumps that instantaneously bridge the distance separating them.) Therefore, any driver who stays as far away from other vehicles as possible is far less likely to collide with one of them than is someone who habitually tailgates or weaves through traffic. And that means that it is methodological nonsense to treat "the odds" for having an accident calculated by treating all drivers as indistinguishable and without influence over the degree of risk they face as if they applied equally to each individual driver.

On the other hand, a passenger on an airplane really does have little he can do to alter the possibility of the plane he is on crashing. (Little but not nothing, e.g., he can refrain from violently taking over control of the aircraft and then deliberately flying it into a building.) In general, this is risk beyond his control, and I see nothing irrational about one being more adverse to such risks than to those one deliberately can control.


  1. You've got to be careful with those comparisons for other reasons, too. E.g. is the right comparison fatality rates per trip, or per mile traveled, or per hour in the vehicle...? It's not obvious how to make it apples to apples, and the safer vehicle can flip depending on which stat you choose.

  2. What if she's male?

  3. Wabulon, did you drop in from a different thread?

  4. Oh, I see, you are commenting on: "To the contrary, any individual driver's likelihood of having a collision is affected quite significantly by how she drives..."

    Well, Wabulon, that's how it's done in academia today -- you alternate "he" and "she" as the neuter human pronoun.

  5. Anonymous6:42 PM

    First the P.C. is B.S. and his (I suppose he could also be a she, but the masculine form is considered by most sane people to be of either sex when written about a generic subject). Second, I think you miss the point entirely in that he was clearly pointing out that there is a distinction between the sexes' driving abilities.

  6. Anonymous12:22 PM

    There is a false premise in this argument. The whole purpose of "odds" is to eliminate individual intangibles to give an overall likelihood of something occuring (or not). Just as an individual's driving prowess may increase his chances of avoiding a traffic accident, an airline's safety record enhances theirs. If you are a fantastic driver with zero violations on your record coming up against a bozo who has 3 drunk driving arrests, bookies will place a bet with odds reflecting the likelihood of the bozo crashing first. But if you (the angel driver) end up crashing first because you had a heqart attack while driving to work, then tough cookies for the bookies, cause they couldn't foresee it and factor it in. When statistics such as odds of dying in a plane crash come out, they measure overall likelihood, but if you parsed the #s between say the record of the safest airlines vs the most reckless, you will find airlines that have been in business for 50+ years (millions of flights) without one casualty (zero), and others that have a major crash every 3-5 years. So yes, you can control your exposure to risk, but your overall odds are the same no matter what you do.

  7. Anonymous8:00 PM

    Very big flaw in the OP's argument. It seems as though you think a person cannot be killed if struck by another person on the road. You may be the best driver on the road, but you're not the only one on it, and could very well be in an accident through no fault of your own.

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