Gentrification — broadly speaking, when more affluent (usually white) people move into an urban neighborhood and price out the previous, less affluent (usually black) residents — is controversial for plenty of reasons, but its effect on crime isn't really one of them. City officials who encourage gentrification tend to take it for granted that gentrification reduces crime.

But academic researchers say that's an oversimplification. A new study suggests that when gentrification occurs as an organic process, then violent crime rates (or at least gang violence) do indeed go down. But if city officials try to force the process by demolishing public housing, it can actually have the opposite effect.

Rent-driven gentrification reduces gang violence...

One way to define gentrification is as a demographic process, generally driven by higher housing prices and rents. You can see that sort of change in the data: lots of white people will move into a neighborhood, or the average socioeconomic status will go up as poorer residents can't afford to live there anymore and more affluent residents move in instead.

as more affluent whites move in, gang violence goes down — but burglary goes up for a while

The author of this study, Chris M. Smith, looked at both these traditional signs of gentrification, and at another one: the growth in neighborhood coffee shops, which can be a very visible symbol that a neighborhood is changing to cater to more affluent people. Smith was particularly interested in the effects of gentrification on gang violence — measured by gang homicides — which is driven by different sorts of factors than other types of crime. In fact, while the overall homicide rate in Chicago went down consistently over the course of the study, the gang homicide rate had significant peaks and valleys. Gang violence is often what local officials fret about in lower-income neighborhoods, or use as a reason to push gentrifying policies.

If you define gentrification as a process of more affluent people moving into a neighborhood and driving up rents, then gentrification does bring with it a substantial decrease in gang violence. If you define gentrification just as how many coffee shops a neighborhood has, the relationship isn't so strong — but there's some correlation there, making it a reasonable symbol of the kind of gentrification that has a positive impact on crime.

There's an important caveat, however. Multiple studies show that as richer people begin moving into a neighborhood, property crimes like burglary begin to rise. Researchers generally assume this is because the new residents of the neighborhood are obvious targets for thieves. But as gentrification continues, the neighborhood eventually calms down again. The trend is basically an upside-down U-shaped curve.

Demolishing public housing doesn't necessarily reduce crime

demolishing public housing is linked to more gang violence

Gentrification isn't always just a real-estate-market-driven process. City governments often encourage it: most aggressively, by tearing down public housing so that developers can build fancier houses on the land. But if cities think this will accelerate gentrification, Smith shows that they're wrong. Demolition of public housing, Smith found, is linked to more gang violence.

It's possible that demolition has the same effect on gang violence that rising rents have on burglary — they rise for a time, as the neighborhood goes through growing pains, then settle down. Smith's study didn't cover quite a long enough period of time to address that. But the study definitely showed that the effects of gentrification on crime can be very different depending on what's driving the gentrifying.