Does immigration decrease crime? Check the stats

Arizonans eager to drive every last illegal immigrant from the state are fond of blaming the undocumented for crime, from beheaded bodies in the desert to a wave of violence that is turning our communities into war zones. It's a potent argument, in that it persists despite an apparent total lack of evidence to support it.

No one has yet found the beheaded bodies that Gov. Jan Brewer told us about; crime rates are flat or down along the border; and reported crime throughout Arizona and the nation is continuing its 15-year decline.

Nationally, for example, the 100 largest metro areas have seen reported violent crime fall 21 percent between 1990 and 2008, while property crime has declined by 42 percent. Murder, sexual assault, robbery, burglary, auto theft—all the major reported crime categories have witnessed large double-digit declines.

In fact, the crime drop has been so steep and prolonged—even continuing through the Great Recession—that leading criminologists confess themselves puzzled—if, of course, pleased. But what if America's drop in crime was caused in part by… immigration? What if the presence of immigrants in a community not only did not increase crime but actually helped decrease it?

Admittedly, it sounds like a stretch. But a 2011 Brookings Institution report, City and Suburban Crime Trends in Metropolitan America, looked at the past two decades of crime data and found that "crime declines significantly with increases in the proportion [of residents] that is foreign-born and Hispanic."

Richard Florida, a professor at the University of Toronto and celebrated author of "The Rise of the Creative Class," says the same.

In recent articles and blog posts, Florida says the crime numbers show that the Hispanic share of the population is negatively associated with urban crime. Further, "the [variable] that is most consistently negatively associated with crime is a place's percentage of foreign-born residents." Florida adds that, "…the pattern held across all of the many, various types of crime—from murder and arson to burglary and car theft."

The Brookings report and Florida's analysis suggest that diversity in general helps decrease crime in a community. But Florida zeroes in on immigrants: "Along with their entrepreneurial energy and their zeal to succeed," he writes, "immigrants are good neighbors — cultural and economic factors that militate against criminal behavior, and not just in their own enclaves but in surrounding communities as well."

Why should increased immigration work against crime? Good question. Unfortunately, concrete answers might be tough to find. The good news: It should be easier than finding those beheaded bodies.