Just Facts: Introducing What Caused The Crime Decline?

Our Justice Program's new report is an interdisciplinary look at increased incarceration's limited role in the last two decades' dramatic crime decline.

March 2, 2015
Prison cell

The Brennan Center’s Justice Program has spent the past year and a half trying to understand mass incarceration, and its role in the crime drop of the past 20 years. Our team of economists, attorneys, and researchers have gathered data, run empirical analyses, reviewed the existing research, attended expert panels, and spoken personally with many researchers and practitioners.

And now we’re excited to share our results with you. Our report — What Caused The Crime Decline? — is an interdisciplinary piece that highlights increased incarceration’s limited role in the drop in crime. Here, and in future posts, we’d like to introduce you to the report and give a first peek into its findings.

Over the past 25 years, the U.S. has undergone two distinct and remarkable changes. One, crime has plummeted. Across crime categories and in every state, crime is significantly lower than it was in the early 1990s. Two, incarceration has continued a steep, steep climb. The incarceration rate has nearly doubled since 1990, and is the highest in the developed world.

It’s natural to draw a causal relationship between these two. A huge swell in incarceration may well have brought down crime. After all, incarceration incapacitates potential offenders, keeping them off the streets, and unable to commit crime. The more people we lock up, the lower crime will be.

But the true story, as true stories often are, is far more complicated. Incarceration may have had a role in reducing crime, yes. But that role was small, and has been shrinking. In essence, incarceration has swelled too much.

Increased incarceration’s role in the crime drop was limited. We find that it was responsible for about 5 percent of the drop in crime in the 1990s, varying statistically from 0 to 10 percent. This is a contribution, to be sure, but lower than what many scholars have found previously. We don’t find any meaningful contribution of increased incarceration to the continued drop in crime in the 2000s.

The reason is simple: an economic concept called diminishing returns. In this case, it is incarceration’s returns, in the form of reduced crime, that have diminished. The more we incarcerated, the less effective it became. In the 1970s, for instance, incarceration may have had a big effect. The levels of incarceration were low, and there may have been a public safety benefit to incapacitating more dangerous offenders. Fast forward to 2000, however. Over a million people have been added to the nation’s prison. Incarcerating more isn’t going to do us nearly as much good. We’ve incarcerated so many people that there are simply fewer people left to incarcerate that would give any meaningful public safety benefit. Incarceration, in a word, is overused.

The report also tries to get a handle on what caused the crime decline. It tries to get a handle of the question, “If not incarceration, then what?”

So, in addition to crime and incarceration, we’ve gathered decades of data on other criminal justice variables (like police employment), demographics, and the economy. This allows us, for one thing, to isolate incarceration’s effect. It also allows us to see if, statistically, these variables are related to crime. We found a modest crime-reducing effect of an aging population, a decline in unemployment, a decrease in alcohol consumption, and increased numbers of police. We also found a significant crime-reducing effect of the policing program CompStat.

We also review some “blockbuster” theories explaining the crime decline. Researchers have suggested that the unleading of gasoline due to the Clean Air Act, and the legalization due to Roe v. Wade, made huge dents in crime. After reviewing the existing research, we believe these may have played some role.

Even still, the crime decline remains largely unexplained — a pleasant mystery. What we have shown, though, is that incarceration does not deserve the credit that it’s often received.

“One of the great problems we face today is mass incarceration,” writes Nobel laureate economist Joseph Stiglitz, in the foreword. We hope our report helps us all better understand the role incarceration plays in our society. It is a role that is limited, but costly.

Check out the report on our website, and over the next few weeks we’ll continue to highlight some of its specific sections, and get into some more detail. What role did other criminal justice factors — like police and policing — play in the crime decline? And what factors or phenomena may have had a large hand in the decline?

(Photo: Flickr/StillBurning)