The difference between “theoretically possible” and “important”

Academics, myself included, love coming up with counterintuitive arguments that change the way people see the world. The media probably loves to publish such articles even more than the academics like to find them.

Sometimes, though, these same academics/media do a big disservice by raising issues that are theoretically possible, but not at all important in reality.

A great example appears in this article in Time magazine about how maybe seat belts don’t save lives because drivers become more reckless when belted because they feel safer. This effect could reduce, or even reverse the safety benefits of seat belts.

The theory is sensible. When I am unbelted, I am at greater risk for injury, so I may drive more cautiously. In economics, this idea is attributed to my friend and colleague Sam “Seatbelt Sammy” Peltzman in the 1970s. Economists call this tendency the “Peltzman Effect.”

In practice, though, the evidence could not be clearer that seat belts are an incredibly cost effective way of saving lives. (See for instance, this study of mine and the citations therein.) Whatever small offsetting impact that more reckless driving due to seat belts may have, it is trivial compared to the benefits of wearing a seat belt. Articles like the one in Time Magazine encourage people to come to completely the wrong conclusion on this question.

If, however, I’m wrong and compensating behavior on the part of drivers really does undo or reverse the benefits of seat belts, there is an easy public policy solution: the government should mandate the installation of a razor sharp knife on every steering wheel aimed directly at the heart of the driver. Just think how carefully we would all drive then.

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  1. pkimelma says:

    The same argument was made about ABS (brakes) years ago. The problem is that even if it is true, the benefits outweigh the costs. Further, one has to remember that many accidents involve a causing driver and one or more victims. So, even if true, the victims are more likely to walk away if they have seatbelts on, ABS, structural cages, and other safety devices.
    As to a knife on the steering wheel, the same victim problem occurs (I know you were not serious, but the concept is the same). If you want that kind of compensating behavior, make it far more costly in other ways to be the “cause” of an accident. Time in jail or community service for example. Of course, then you get far more lies and disputes and paid off witnesses, etc.

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  2. pkimelma says:

    The same argument was made about ABS (brakes) years ago. The problem is that even if it is true, the benefits outweigh the costs. Further, one has to remember that many accidents involve a causing driver and one or more victims. So, even if true, the victims are more likely to walk away if they have seatbelts on, ABS, structural cages, and other safety devices.
    As to a knife on the steering wheel, the same victim problem occurs (I know you were not serious, but the concept is the same). If you want that kind of compensating behavior, make it far more costly in other ways to be the “cause” of an accident. Time in jail or community service for example. Of course, then you get far more lies and disputes and paid off witnesses, etc.

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  3. John Hawks says:

    I’m really surprised that you think that your article answers the points raised by Adams. He *doesn’t* claim that seat belts make their wearers less safe in a crash, or that the majority of people who wear seat belts will be more likely to drive aggressively.

    His claims are about the global costs of seat belt laws: (1) Drivers have a “risk thermostat” that makes some people likely to drive more aggressively when they adopt risk prevention devices such as seat belts. Those people make the road globally more dangerous, even for safe drivers. (2) Saved lives on the part of drivers and passengers are offset by costs to the system that aren’t counted in the same way, such as pedestrian and cyclist fatalities.

    You are quite right that razor blades on the steering wheel would improve road safety; Adams makes the same point. You seem to agree.

    You disagree (apparently) about the safety statistics following the adoption of seat belt laws, but your data doesn’t address the international comparisons (countries with and without laws, and effects on individual countries after adopting seat belt laws) that Adams presents in his 1995 book.

    Frankly, I think this is a ripe topic for the Freakonomics treatment — his international seat belt comparisons are similar in form to the abortion data, with the advantage that there is no 18 year delay.

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  4. John Hawks says:

    I’m really surprised that you think that your article answers the points raised by Adams. He *doesn’t* claim that seat belts make their wearers less safe in a crash, or that the majority of people who wear seat belts will be more likely to drive aggressively.

    His claims are about the global costs of seat belt laws: (1) Drivers have a “risk thermostat” that makes some people likely to drive more aggressively when they adopt risk prevention devices such as seat belts. Those people make the road globally more dangerous, even for safe drivers. (2) Saved lives on the part of drivers and passengers are offset by costs to the system that aren’t counted in the same way, such as pedestrian and cyclist fatalities.

    You are quite right that razor blades on the steering wheel would improve road safety; Adams makes the same point. You seem to agree.

    You disagree (apparently) about the safety statistics following the adoption of seat belt laws, but your data doesn’t address the international comparisons (countries with and without laws, and effects on individual countries after adopting seat belt laws) that Adams presents in his 1995 book.

    Frankly, I think this is a ripe topic for the Freakonomics treatment — his international seat belt comparisons are similar in form to the abortion data, with the advantage that there is no 18 year delay.

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  5. Bill Conerly says:

    Hey, there’s a tradeoff between safety and speed (with “speed” being a proxy for speed, recklessness, drunkenness, etc.). When there’s an improvement in the opportunities open to me, and I choose to load all of the gains into speed, leaving safety unchanged, what’s wrong with that? I get to drive faster. I’m better off. So what if I didn’t use the gains in the way you would like me to; it’s my choice to make.

    Whether I use seat belts to reduce my risk or to increase my speed, there is still a gain from wearing seatbelts.

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  6. Bill Conerly says:

    Hey, there’s a tradeoff between safety and speed (with “speed” being a proxy for speed, recklessness, drunkenness, etc.). When there’s an improvement in the opportunities open to me, and I choose to load all of the gains into speed, leaving safety unchanged, what’s wrong with that? I get to drive faster. I’m better off. So what if I didn’t use the gains in the way you would like me to; it’s my choice to make.

    Whether I use seat belts to reduce my risk or to increase my speed, there is still a gain from wearing seatbelts.

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  7. John Hawks,

    I probably could have made my logic clearer. My point was that seat belts have huge direct effects on safety. I can imagine they also have small indirect effects through the Adams channel, but it is totally implausible
    to me that wearing seat belts would lead to nearly a doubling in serious crashes, which it is what it would take to offset the direct effect.

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  8. John Hawks,

    I probably could have made my logic clearer. My point was that seat belts have huge direct effects on safety. I can imagine they also have small indirect effects through the Adams channel, but it is totally implausible
    to me that wearing seat belts would lead to nearly a doubling in serious crashes, which it is what it would take to offset the direct effect.

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