Thursday, August 13, 2009

S-A-F-E-T-Y Math

I have always adored Laurie Anderson, and her piece entitled New Jersey Turnpike has long been one of my favorites:
He said, you know, to be really safe you should always carry a bomb on an airplane. Because the chances of there being one bomb on a plane are pretty small. But the chances of two bombs are almost minuscule. So by carrying a bomb on a plane, the odds of your becoming a hostage or of getting blown up are astronomically reduced.
I've always enjoyed that passage at a number of levels, but the pertinent point here is the statistical misunderstanding. In this case, if a given passenger has brought a bomb onto a plane, the probability of a second passenger also having a bomb is unchanged; the two (possible) occurrences are said to be independent. If you just rolled a die and got a six, the probability of rolling a second die and getting a six is just the same as if you hadn't rolled the first die; again, the two events are independent. So carrying a bomb onto a plane, one that you will not detonate because you don't want to die, has absolutely no effect on the probability that someone else, with evil intentions, will.

It does, however, drastically increase the probability that a bomb will accidentally destroy your flight.

Now I don't really expect the wingers to understand probability and statistics. I'm not going to claim that I really understand the topic; it's often counter-intuitive, and it's often badly misused. I just wish more people had a sense of common techniques for how they're misused. Such an understanding might put an end to this sort of frightening nonsense. From Gail Collins' column today:
We are getting yet another series of reminders of the vast gun gap in this country. There is the part that thinks a room full of red-faced men and women screaming at one another is the worst place in the world to bring a firearm. And then there is the part that holds it is exactly the place where you need it most. “A firearm is a defensive tool,” said Kostric, in an interview with Chris Matthews on MSNBC. He was wearing a yellow T-shirt, and he told Matthews that if everybody in the crowd waiting for Obama to arrive had been armed, things would have been much safer.
I was just skimming over Anderson's Wikipedia article to see if it was worth linking, and found this very appropriate bit of trivia to tack onto this post. Her first single was entitled, "It's Not the Bullet that Kills You (It's the Hole)."

So there's the bottom line: Guns don't kill people, holes do. In this case, it's the holes between too many people's ears.

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