How homicide spreads like an infectious disease

The Gangs of New York:
An Informal History
of the Underworld

by Herbert Asbury

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Powell's Books
I remember reading the 1927 book, Gangs of New York by Herbert Asbury and thinking of how the circumstances of poverty and crowding led to so much of the development of gangs, starting with groups of immigrant thugs and bullies and ending up many years later with the Mafia and other "professional" crime groups.

If you haven't read Asbury's book but have seen the movie, while a few of the historical characters (yes, Bill the Butcher was a real person) ended up in the Martin Scorsese movie, unlike the movie, the book is an "informal" history of people living in the Five Points slum of New York.  

Jump forward to today and we still have far too many marginalized youth living in or near poverty who feel the gang life is their only way to achieve anything.  This doesn't excuse their acts, but it does explain how they get to where they are.

This story is another example of how statistical techniques combined with a computer can be put to use to predict patterns of criminal and anti-social behavior - and perhaps giving us a handle on the problem.

Here's the report, again with a link to the original studies in the attribution lines.
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Can science predict gang killings?

"In the places gang homicides move into, we see other types of homicide
-- specifically, revenge and drug-related killings -- also clustering."

Gang slayings move in a systematic pattern over time, spreading from one vulnerable area to the next like a disease, finds a groundbreaking study by Michigan State University criminologists and public health researchers.

Their findings, published online in the American Journal of Public Health, could help pave the way for communities to one day anticipate and ultimately prevent gang-related homicides and other violent crimes.

Gang membership growing nationally
There were 2,363 gang-related killings in the United States in 2012, the highest number in at least six years, according to the latest available estimates from the Department of Justice. Gang membership also increased, to 850,000 in 2012 from 788,000 in 2007.

"We've shown that there is a potentially systematic movement of gang-related homicides," said April Zeoli, associate professor of criminal justice and lead investigator on the study. "Not only that, but in the places gang homicides move into, we see other types of homicide -- specifically, revenge and drug-related killings -- also clustering. Taken together, this provides one piece of the puzzle that may allow us to start forecasting where homicide is going to be the worst -- and that may be preceded in large part by changes in gang networks."

Using police data from Newark, New Jersey, Zeoli and fellow MSU researchers Sue Grady, Jesenia Pizarro and Chris Melde were the first to show, in 2012, that homicide spreads like infectious disease. Similar to the flu, homicide needs a susceptible population, an infectious agent and a vector to spread. (The infectious agent could be the code of the street -- i.e., guarding one's respect at all cost, including by resorting to violence -- while the vector could be word of mouth or other publicity, Zeoli said.)
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Juvenile gang members in US top 1 million, new study finds
There are over one million juvenile gang members in the U.S., more than three times the number estimated by law enforcement, according to a recent study.  "Gang membership between ages 5 and 17 years in the United States," published in the Journal of Adolescent Health, challenges many popular demographic stereotypes about gangs.
The study found that an average of 2 percent of youth in the U.S. are gang members, with involvement highest at age 14, when about 5 percent of youth are in gangs. Youth in gangs also come from all types of backgrounds.
"The public has been led to believe that gang members are black and Latino males and that once someone joins a gang they cannot leave a gang, both of which are patently false," said David Pyrooz, assistant professor of Criminal Justice at Sam Houston State University.
"Being a gang member is not all that it is cracked up to be, which is something kids realize once they get involved and find out that the money, cars, girls, and protection is more myth than reality," said Pyrooz.
Source:  Materials provided by Sam Houston State University. David C. Pyrooz, Gary Sweeten. Gang Membership Between Ages 5 and 17 Years in the United States. Journal of Adolescent Health, 2015
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With the new study, the interdisciplinary team of researchers analyzed the Newark data to gauge whether specific types of homicide cluster and spread differently. In addition to gang-related murders, the researchers looked at homicide motives such as robbery, revenge, domestic violence and drugs. These other motive types were not directly connected to gang participation.

The study found that the various homicide types do, in fact, show different patterns. Homicides stemming from domestic violence and robberies, for example, show no signs of clustering or spreading out.

"Gang-related killings were the only type of homicide that spread in a systematic pattern."

Gang-related killings were the only type of homicide that spread in a systematic pattern. Specifically, there were four contiguous clusters of gang-related homicides that started in central Newark and moved roughly clockwise from July 2002 through December 2005.

Revenge and drug-motivated homicides unrelated to gang activity did not spread out, but they did cluster. Interestingly, they clustered in the same general area as the gang murders.

"By tracking how homicide types diffuse through communities and which places have ongoing or emerging homicide problems by type, we can better inform the deployment of prevention and intervention efforts," the study says.

Related stories:
Story Source:  Materials provided by Michigan State University. April M. Zeoli, Sue Grady, Jesenia M. Pizarro, Chris Melde. Modeling the Movement of Homicide by Type to Inform Public Health Prevention Efforts. American Journal of Public Health, 2015


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