Cholera, Influenza and Murder

Morning Edition:

Zeoli recently decided to test that theory using the lens of public health research: When scientists study the outbreak of an infectious disease like AIDS or the flu, they don't ask what it is about specific individuals that made them sick. They look for broader patterns, knowing that illness in any individual stems from a process of contagion.
Along with colleagues Jesenia M. Pizarro, Sue C. Grady and Christopher Melde, Zeoli asked whether homicide might follow the same principles of contagion.
"We looked at homicide as an infectious disease," Zeoli said in an interview. "To spread, an infectious disease needs three things: a source of the infection; a mode of transmission; and we need a susceptible population."
The researchers studied every homicide that occurred in the city of Newark, N.J., over a period of a quarter century, from January 1982 to September 2007. In all, Newark had seen 2,366 murders in that period, a rate of homicide some three times as high as that of the general U.S. population.
The researchers tracked down the time and location of every single murder. They plugged the data into a software program that has previously been used to track infectious diseases: When you put in the geographical location and the time of infection of each victim of the infectious disease, the program creates a model that shows how the epidemic is spreading — and where it might go next.
"We hypothesized that the distribution of this crime was not random, but that it moved in a process similar to an infectious disease, with firearms and gangs operating as the infectious agents," the researchers wrote in a paper they published in the journal Justice Quarterly.
The analysis showed that homicide spread through Newark very much like an infectious disease. The value of tracking murder in this fashion, Zeoli said, was not just to let police know where murder was happening — police already track hot spots and direct resources to those areas — but to make predictions about where homicide might spread next, based on the path of the epidemic.
Zeoli said that the model could make specific predictions about how and where homicide would spread in the future — information that could prove very valuable to police and other city officials.

I'm not extremely surprised by this.  I think a lot of things work along these lines.  Social influence causes people to act in certain ways, good and bad.  For another example, sometimes teen suicides come in little groups.  One action ends up making similar actions more acceptable.