We’ve touched on this before: Since the mid-1990s, violent crime across the United States has dropped dramatically. DC has gone from several hundred murders per year a decade ago to 108 last year.
And yet, experts struggle to explain the drop. Charles Murray, of the American Enterprise Institute, argues that the answer is actually simple: widespread policies of mass incarceration have taken thousands of criminals off the streets, which both removed violent people from neighborhoods and created a deterrent.
The blue line shows violent crime per 100,000 people. The red line shows prisoners per 1,000 violent crimes.
So how much of the reduction in violent crime was produced by increased incarceration? This kind of analysis doesn’t tell us. But neither am I sure that the armory of social science quantitative techniques adequately models what has gone on. Here is my simple-minded thought: Suppose we had maintained imprisonment for violent crime at the rate that applied in 1974. In that case, we would have had 276,769 state and federal prisoners in 2010 instead of the 1,518,104 we actually had. Suppose tomorrow we freed 1.2 million inmates from state and federal prisons. Do we really think violent crime would continue to drop at a somewhat slower pace?
In one sense, it is a silly question, as all counter-factuals must be. And I’m not saying that our current incarceration rates are appropriate. We may very well have been in a state of diminishing returns to incarceration for the last decade, as the experts DiIulio cites have argued. But I continue to harbor the belief that without the massive increases in incarceration after the mid 1970s, crime rates wouldn’t have turned around at all. Higher imprisonment was the necessary condition for 100 percent of the reduction in violent crime.
John Roman of MetroTrends calls this a mathematical slight of hand. The blue line in Murray’s chart, he argues, actually shows that incarceration is becoming less effective:
Because it is the ratio of prisoners to violent crime, the blue line is the number of people we incarcerate per 1,000 violent crimes. Violent crime is tragic, but we, as a society, want that line to be as low as possible. The lower the line is, the less we are spending per violent crime. The line is at its minimum in the late 1970s until 1980—just prior to America’s incarceration binge. That the line goes up after 1980 is not a good thing, as Murray would have you believe, but a very bad thing—it’s what economists refer to as diminishing marginal returns to imprisonment. Every year since 1980 we have had to lock up a lot more people to maintain the same amount of violence, which means prison is getting less and less cost effective.
