Blog Ipsa Loquitur

From this essay by Federal Judge Jed Rakoff on the sociological destructiveness of mass incarceration, a brief detour into the statistics of crime prevention:

There are some who claim that they do know whether our increased rate of incarceration is the primary cause of the decline in crime. These are the sociologists, the economists, the statisticians, and others who assert that they have “scientifically” determined the answer. But their answers are all over the place.

Thus, for example, a 2002 study by the sociologist Thomas Arvanites and the economist Robert DeFina claimed that, while increased incarceration accounted for 21 percent of the large decline in property crime during the 1990s, it had no effect on the similarly large decline in violent crime. But two years later, in 2004, the economist Steven Levitt – of Freakonomics fame – claimed that incarceration accounted for no less than 32 percent of the decline in crime during that period.

Okay, so everyone agrees that crime has been declining since about the late 1980s or early 1990s. But nobody’s really sure why. There are some economists who think that mass incarceration is responsible for about 20-30% of that drop. Not a majority at all, but a signifcant amount for sure. Heck, 30% might even be a plurality, or near to it.

It’s also probably not accurate:

Levitt’s conclusions, in turn, were questioned in 2006, when the sociologist Bruce Western reexamined the data and claimed that only about 10 percent of the crime drop in the 1990s could be attributed to increased incarceration.

Wait, so the same “crime is lower” data either supports a 30% attribution or a 10% attribution to mass incarceration? That’s eyebrow-raising. What if the SATs were graded with a 20% margin of error? What if your car’s speedometer was 20% off?

But two years after that, in 2008, the criminologist Eric Baumer took still another look at the same data and found that it could support claims that increased incarceration accounted for anywhere between 10 percent and 35 percent of the decrease in crime in the 1990s.”

A group of researchers at New York University Law School also came up with numbers as low as “less than one percent” for the amount of the drop in crime which could be attributed to mass incarceration. So, you know. It might have nothing to do with putting tons of people in jail.

Here’s a helpful hint: countries like Germany and the Netherlands, which do not imprison young men nearly as much as America does, have seen roughly the same rate of decline in crime as America has. That’s not completely dispositive, but that’s pretty damning.