Before The Interrupters, Alex Kotlowitz brought CeaseFire to the nation's attention with a profile of Gary Slutkin, and his appealing idea: that violence spreads like a disease, and should be approached as an epidemiologist looks at the problem. And Kotlowitz's profile came at a critical time, the last time homicides in many major cities rose after years of decline:

THE STUBBORN CORE of violence in American cities is troubling and perplexing. Even as homicide rates have declined across the country — in some places, like New York, by a remarkable amount — gunplay continues to plague economically struggling minority communities. For 25 years, murder has been the leading cause of death among African-American men between the ages of 15 and 34, according to the Centers for Disease Control and Prevention, which has analyzed data up to 2005. And the past few years have seen an uptick in homicides in many cities. Since 2004, for instance, they are up 19 percent in Philadelphia and Milwaukee, 29 percent in Houston and 54 percent in Oakland. Just two weekends ago in Chicago, with the first warm weather, 36 people were shot, 7 of them fatally. The Chicago Sun-Times called it the “weekend of rage.” Many killings are attributed to gang conflicts and are confined to particular neighborhoods. In Chicago, where on average five people were shot each day last year, 83 percent of the assaults were concentrated in half the police districts. So for people living outside those neighborhoods, the frequent outbursts of unrestrained anger have been easy to ignore.

Slutkin's work focuses on individual transmissions, and CeaseFire attempts to stop crimes incident by incident, stopping escalation before it turns into a shooting, less like a vaccine than a general-care physician. But it's not the only way to look at violence; just as people can infect each other, neighborhoods can infect each other. This is one of the concerns in Chatham and Avalon Park, as Robert Sampson wrote in Great American City:

Unfortunately, predominantly black neighborhoods in Chicago, whether poor, working class, or middle income, have always faced spacial vulnerability to crime to an extent that white neighborhoods of all kinds simply have not. Consistent with the theme of racially uneven exposure, the twenty-year-old man shot while attempting to rob Officer Wortham did not live in the neighborhood, but came from a nearby South Side community, the Wentworth Gardens area just west of the former Robert Taylor Homes [Wentworth Gardens lies between U.S. Cellular Field to the north and the very disadvantaged Fuller Park area to the south.] Another apprehended robber came from Englewood, the extremely distressed community to the west of the expressway. Global effects of concentrated disadvantage and spacial vulnerability have been described in earlier chapters, but in this tragic story we see the confluence of mechanisms at work in a single local community. Will Avalon Park and Chatham become the new truly disadvantaged as the black middle class flees, more houses are foreclosed, and poverty rises with the influx of families displaced by the city's housing authority?

At the Urban Institute, John Roman applies the epidemiological theory of violence to this bird's-eye perspective, and looks at what happens when economic segregation puts poor neighborhoods (like Englewood) in proximity to middle-class but vulnerable neighborhoods (like Chatham)—where the middle class serves as a buffer between the rich and poor. If you accept the theory behind it, the results are interesting:

The answer is surprising. While we know that isolating our poorest residents is really bad for them, it turns out that segregating the rich and poor leads to the worst outcomes for a city as a whole. Economic integration, where the rich and poor live side by side, leads to the safest cities.

To test this hypothesis, I have borrowed some Brookings Institution models describing the spread of viruses. Working with our DC Crime Policy Institute, the Brookings scholars determined that at least 70 percent of crime in Washington, DC, is due to contagion (the spreading of crime like an epidemic).


When you work through the entire epidemic, you find that the 25 infected neighborhoods infect an additional 17 neighborhoods. By segregating and isolating the most at-risk places, crime is not corralled, but rather spreads more effectively.

It actually shouldn't be that surprising, if you've played games like Go or Game of Life. The more vulnerable neighborhoods that border violent neighborhoods, the greater the odds that more neighborhoods will flip. Roman's model is very abstracted—other than the research of his colleagues, it's just math. So proceed with caution, but it's an interesting way of literally reframing the debate. Unfortunately, while there have been modest successes with adding mixed-income housing to good neighborhoods, we really don't know much, or have much experience with, turning bad neighborhoods around.