Wednesday, June 18, 2008


There are two articles in the July/August 2008 Atlantic (Monthly) that I found really interesting. One tries to explain the recent rise of the murder rate in some American cities, while the other argues that street signs make us less safe, rather than more safe.

In the first article, Hanna Rosin explores why cities like Memphis have seen a spike in murders. Memphis, as described in the article, has seen crime spike in areas where it had not been before. It also saw crime fall dramatically in areas where it had been a problem. Now police forces are misaligned, since crime is no longer where the police are. Oh, and like so many cities, Memphis tore down its projects.

Lo and behold, it turns out that when you track the displaced residents from the former projects, it turns out that the spike in crime correlates to the location of displaced people. In other words, there was nothing intrinsicly violent about the project buildings themselves. Instead, it turns out that a certain percentage of the residents of the projects were violent thugs, and remained violent thugs after they were displaced from the projects. Seriously, it took Memphis years and two professors to figure this out. Now, we can have debates and discussions about the underlying cause of the thuggery, but good God, this is incredible.

UPDATE: As pointed out in the comments, there are people who think the Atlantic article is off base for a variety of reasons. First, correlation is different from causation, and second, slightly tweaking the data to reflect crime rate rather than criminal incidents may undermine the apparent correlation. That's all fine, but all it really means is that the Memphis data is used to prove too much. That being said, I invite the authors to buy a house in Maywood next to some Section 8 housing with people displaced from the CHA projects living there. Let us know how that works out. They'd be better off moving 100 feet from Cabrini-Green.

In the second article, John Staddon argues that stop signs and speed limits actually make our roads less safe. I believe that a fair summary of this thesis is that all of the thousands of stop signs, and ever-varying speed limits (a) distract people from driving, and (b) give people a false set of expectations regarding the driving behavior of others. In other words, the "defensive driving" theory we all learned to drive with is eroded by the pure amount of signage out there.

Apparently in the UK there are many fewer traffic signs, including many fewer speed limit signs, and very few stop signs. This leads to fewer traffic fatalities per million people (so it is not a function of the US having more people). The theory is that the UK lets drivers . . . drive. They pay attention, and they do not have a false sense to security with all of the signs. When there is a sign, people take it seriously because signs are so rare. The article basically says that this model could and should work in the US as well.

There are a few things here. First, with regard to point (b), I have argued for years that people would drive more safely if safety glass, seat belts, air bags, and anti-lock brakes were removed. They would drive yet more safely if insurance, rather than being universal, were against the law. The risk of driving would skyrocket, and people who did it would be very, very careful. However, I strongly suspect that rationale (a) (i.e. we are all distracted reading signs) is almost certainly wrong, and that the fact that we ignore so many signs directly leads to (b) in that others expect us to have read the signs. To that extent, getting rid of many of the overly informational signs may actually make us safer.


Anonymous Alex McNamara said...

Hey, here is a great rebuttal to the Rosin article. The blog name is a bit cheesy, but the content seems pretty solid.


8:35 PM  

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