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What Bothers People About SuperFreakonomics?

We never know what parts of our books will agitate people enough that they will send us an email. In Freakonomics, the passages that inspired the most emails were the discussions of swimming pools vs. guns and real estate agents not always acting on behalf of their clients.
In SuperFreakonomics, far and away the most common subject of emails is drunk walking vs. drunk driving. In particular, every few days someone writes us to tell us that our analysis is wrong because we are comparing the rate of death per mile driven drunk versus the rate of death per mile walked drunk. Sure, they say, drunk walkers get killed more per mile. But since cars travel much faster, per hour, it is safer to drive drunk than to walk drunk.
It is true that if someone held a gun to your head and said, “If you don’t walk drunk for an hour or drive drunk for an hour, I will shoot you. You choose whether you would walk or drive,” then you might very well want to spend your hour walking drunk. However, in real life, that is virtually never the dilemma you face. Rather, you are drunk in one place and you want to get to another place. The distance you need to cover is what is constant, not the time you will spend traveling.
Thus the per-mile comparison we make is the most sensible one.
The other thing about that passage that makes people angry is that they interpret our arguments as condoning drunk driving, despite the fact that we cite my own research that shows that drunk drivers are 13 times as likely to cause a fatal crash. We end by telling people to take a cab.
When we wrote that people should take a cab, however, we never actually did the calculation. Is it really true that taking a cab is the right thing to do?
According to our estimates, there are 21 billion miles driven drunk each year, resulting in 13,000 fatalities. That works out to be about one fatality for every 1.6 million miles driven drunk.
Economists typically use a value per statistical life of $6 million. So, for instance, when trying to decide whether the benefits of a government program outweigh the costs, the benefit per life saved is calculated as being worth $6 million. If one person dies for every 1.6 million miles driven drunk, and the value of a life is $6 million, then the cost in extra deaths per mile driven drunk works out to be about $3.75.
That number is an average. Obviously, it will depend on how drunk you are, and it ignores other risks associated with driving drunk like getting arrested.
How much does it cost to take a cab? According to this web site, a three-mile cab ride will cost you about $8 plus tip in most major cities. After a tip, that is about $3 per mile — not too different than the implied cost per mile of driving drunk.
Obviously, I’ve left out all sorts of other costs and benefits in this simple analysis that could tip the balance one way or another, but I suspect most people will be surprised to see how close it is to a toss-up.