Do gun bans work?

Steven D. Levitt at the Freakonomics blog says No More D.C. Gun Ban? No Big Deal. Levitt makes the point that the primary reason for having bans is to lower crime but then he asks Do they actually work? He writes

There is remarkably little academic research that directly answers this question, but there is some indirect evidence.

He starts by looking at the direct evidence, such as it is. Levitt writes

The fundamental difficulty is that you have one law change. So you can compare D.C. before and after. Or you can try to find a control group and compare D.C. before and after to that control group before and after (in what economists call a differences-in-differences analysis).

The problem here is that crime rates are volatile and it really matters what control group you pick. I would argue that the most sensible control groups are other large, crime-ridden cities like Baltimore or St. Louis. When you use those cities as controls, the gun ban doesn’t seem to work.

But what about the indirect evidence? Here Levitt explains

What about indirect evidence? In Chicago we have a gun ban and 80 percent of homicides are done with guns. The best I could find about the share of homicides done with guns in D.C. is from a blog post which claims 80 percent in D.C. as well. Nationwide that number is 67.9 percent, according to the F.B.I.

Based on those numbers, it is hard for someone to argue with a straight face that the gun ban is doing its job. (And it is not that D.C. and Chicago have unusually low overall homicide rates either.)

It seems to me that these citywide gun bans are as ineffective as many other gun policies are for reducing gun crime. It is extremely difficult to legislate or regulate guns when there is an active black market and a huge stock of existing guns. When the people who value guns the most are the ones who use them in the drug trade, there is next to nothing you can do to keep the guns out of their hands.

Here I think Levitt has a point, gun bans don't effect those who use guns in crime. People who want a gun for criminal purposes don't care if there is a gun band, since they are not likely to use the legal market for getting a gun. If you are a drug dealer, and want a gun, you get it illegally so a gun ban doesn't effect you.