Gang “homicides spread like infectious disease”; other homicides do not

A new study adds to the social network analysis of gang activity by comparing clusters of gang homicides to other kinds of homicides:

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.)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. 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.

Such findings, adding to previous research showing a relatively small cluster of gang members in a big city can be responsible for a large number of homicides, should help lead to better prevention and policing efforts. All homicide is not alike as the root causes and people involved can differ.

Two other things are interesting about this coverage:

1. The medical analogy – an infectious disease that needs to be cured – is likely to be appealing to a broad number of people. This might work better than the rhetoric of needing to find the killers and lock them up.

2. The headline of the story is “Can sociology predict gang killings?” and one quote in the story might provide evidence for this: “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.” However, forecasting where homicides are more likely to happen is not exactly the same as predicting gang killings.

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