no seriously, don't profile

Sarcasm may have obscured the point of the last post. Profiling makes even less sense against organized terrorists than against criminals. Why? The age/ethnic mix of terrorists that we see now is in part a reaction to the security that they'll face. If young men are always searched then female suicide bombers will be recruited, and the defenses will be worse off than if they screened passengers randomly. This isn't just a game theory exercise:

On April 17 1986, a young woman presented herself at Heathrow's gate 23 for that morning's El Al flight to Tel Aviv. She had cleared the airport's own security check-in procedures, but to El Al's security staff something didn't appear right. A search of her hand luggage revealed 1½ ounces of Semtex and a detonator, hidden in a calculator.

The young woman was Anne Murphy, a white, Catholic girl from Dublin. The explosives had been planted by her boyfriend, Nezar Hindawi, a terrorist with links to the Syrian government.

Of course, I'm starting to give the impression that we should worry about terrorism, when in fact doing so has surpassed the war on drugs as one of the worst acts of collective hysteria since McCarthyism. For example, think of dying prematurely as an enormous waste of time (like reading blogs! but worse.) The average adult has about 300,000 hours of waking life to expect, and a 1 in 13,000,000 chance of dying on the average U.S. domestic flight (this was true in 1990-1999 entirely from accidents, and in 2000-present almost entirely from 9/11, as there's been only one fatal accident during that time. Your chance of dying on a developing world flight is 1 in 1.5 million, regardless of carrier. These and other fascinating facts found here). If you're risk-neutral, avoiding this risk should be worth two minutes of your time. By this argument, two minutes is also a good baseline for the amount of time that airport security should be willing to waste per passenger. The last point is the crudest part of the argument and shouldn't be stretched too far, since it's based on the risks we currently see, which might change in the extreme case of airports completely eliminating screening. Needless to say, I think we're far from that point. (Incidentally, google for probability terrorism dying to see how a little math knowledge can be an upsetting thing.)

The time vs. death comparison seems a generally useful one because it avoids all the problems in comparing lives with money. Another place it's obviously relevant is in speeding. The probability of dying while driving is supposedly proportional to the fourth power of your speed. In the U.S., drivers die at a rate of about 15 per billion miles and are seriously injured at about 10 times that rate. If we assume the fourth-power law and that everyone is driving 65mph (assume a spherical cow...), then increasing speed by 1mph will save 0.84 seconds/mile and increase the chance of being killed/mile by about 9.2 x 10^-10. Multiply by 300,000 hours and you get just about one second, which is pretty close to the amount of time saved. To account for injury, one method is to examine the number of disability-adjusted life years (DALY's) lost. In 2002, 1.18 million died in traffic accidents and 38.4 DALY's were lost, which comes to about 33 DALY's/death. This means my "50 years/death" was an overestimate and increasing 1mph actually costs closer to 0.65 "disability-adjusted life seconds"/mile. Even if we assume there's another car involved half the time, this is close to a tie, meaning that 65mph is close to optimal. On the other hand, this still hasn't included property damage (which ranges from 1% of GNP in developing countries to a stunning 2% in rich countries), higher gas consumption and the fact that speeding tickets waste time too. So I think this means that

1. we shouldn't speed Moderate speeding is a little dangerous, but not unreasonably so.
2. Applying the 300,000 hours argument to airline security can't be totally absurd since it leads to different conclusions in different contexts.
3. I should stop wasting so much time writing silly blog posts.

p.s. I look forward to Ilya's theory of driver safety profiling in the comments!

Update: Thanks to Aaron in the comments for pointing out mistakes in my driving calculations (now corrected); I had represented driving as 10 times more dangerous than it actually is.