If you look at this chart, it's not hard to think that the great crime drop was caused by locking up all the criminals. A student brought this up in class. In the 1990s, it looks pretty convincing:
But just looking at the 1990s misses the big picture. Here's the same data going back to 1925. Crime went up and down and up and down, but the prison rate stayed more or less the same, and then skyrocketed after 1970.
And here's what happens it you look at each decade separately:
What it comes down to is this:
In three decades we've had more prison and more murders. In two decades we've had more prison and murders were basically unchanged. In one decade we had less prison and less murder. And in just one decade, the 1990s, we've had more prison and less murder.
Between 1947 and 1991, the prison population increased almost 500 percent. Meanwhile the homicide rate went up by more than a third. Did locking up more people increase the homicide rate? Probably not.
So what makes the 1990s the decade of choice that proves incarceration is the solution to crime? Was there some magic tipping point? Was there something special about the second million we incarcerated that didn't apply to the first million? Probably not.
I'll put it another way, in 1947, the homicide rate was 6.1 per 100,000 and we had 259,000 people behind bars. In 2007, we had the same murder rate of 6.1 and yet 2.3 million people are behind bars. What good have we gotten from locking up an extra two million people, spending something like $50 billion per year for the privilege?
You think there might be a better way?