This shows that violent crime, which has been dropping for decades now, continued its sharp descent over the last few years, at least until 2011. Judge Kopf’s considered opinion is that “harsh sentencing” has a lot to do with this. The idea, as fleshed out by Judge Kopf in the comments to his post, is that longer sentences keep more criminals off the streets, where they can’t commit crimes (except against each other). Judge Kopf also cites with approval the idea that “the graying of America” has lowered the crime rate because old people don’t commit as much crime as young people. Thus, a shift to an older population will reduce the crime rate.
I think it is pretty easy to show that these two arguments (mass incarceration and the greying of Amercia) are not responsible for much of the epic drop in the crime rate. To do so, let’s assume that these arguments explained 100% of the drop in the crime rate. We would expect to see at least two things in the data.
1) We’d expect that the youth crime rate would be relatively stable. This is because the "graying of America" argument assumes a stable crime rate within age groups, and the "mass incarceration" argument assumes that we are imprisoning people longer (but not sooner). Thus, neither of these arguments can explain any appreciable drop in the youth crime rate.
2) To whatever extent other factors might affect the crime rate, we’d still expect that the crime rates of people in middle age would drop more than the crime rates of youth. This is because the mass incarceration argument assumes that we are sweeping up new criminals and keeping them in jail, where they can’t commit any crimes (except against each other). Before the “draconian” sentencing policies, we let those people out of jail, at least sooner, so they presumably used to drive up the crime rate of the middle aged when they got out of jail and went back to their evil ways.
But here are the facts: the youth crime rate has plummeted, and the middle-aged crime rate hasn’t. This FBI report tells the tale. It breaks down the crime rate by age for every year between 1993 and 2001. (I can’t find the data for other years, but this is a good date range because it encompasses the first half of the great crime rate drop, which started in earnest in 1995.)
Focusing on the violent crime rate, we can see that it has plummeted among the very young, merely lessened among the not-so-young, and not dropped at all among the middle-aged:
Now, you might be wondering what has happened since 2001. So I did a little work to figure this out. I found the statistics from the 2010 census, which break down the population by age. Then I calculated a violent crime rate for each of the above age groups using the FBI crime data from 2010. Here’s the result:
Given these numbers, it’s hard to believe that the graying of the US population has had more than a trivial effect on the crime rate. On the contrary, the drop in the crime rate is overwhelmingly a youth phenomenon. Kids these days—they’re just way better behaved than they used to be. And they keep getting better! They are less than half as likely to commit a violent crime than their forebears from my generation. That is astounding, and demographics cannot explain it.
These numbers also undercut the argument that mass incarceration is a big factor in the crime rate drop. The mass incarceration argument is that the crime rate is dropping because we’re locking up all the bad guys. But these numbers show definitely that there are just fewer bad guys to lock up.
Of course mass incarceration could have had a nice healthy side effect: deterrence. It could be that tough-on-crime policies have scared the bejeezus out of kids. Kids who once were willing to steal a car when it meant just five years in jail are saying “no way!” when it means ten years in jail.
Anyone who’s spent much time around young men knows that this is argument is unlikely to be true. Young men don’t weigh consequences very well, which is why they are vastly more likely to commit crimes in the first place. So changing the incentives at the margin probably doesn’t matter much.
So what does explain this? My favorite theory remains: lead.