On June 10th, 2011, Dallas Drake, Principal Researcher for the Center for Homicide Research, presented a paper at the Homicide Research Working Group in New Orleans, Louisiana outlining the discovery of cyclic patterns between occurrences of homicide. In an earlier paper by Drake and co-authors, Charles Crain and Jessica Proskin, also Center researchers, a similar pattern was discovered using data from Flint, Michigan.
The methodology used to discover these patterns is unique. It consists of plotting the temporal interval between each homicide and then placing it in a visual medium. Researchers using Contagion Theory then extracted non-contagious homicides (non-firearm homicides) from those thought to be contagious (firearm homicides).
Patterns were immediately evident. Contrary to the theory however, non-contagious cycles were also observable, though at a different scale of measure. This means that the reason these interval cycles had never before been detected is that the two patterns were overlapping, thus obscuring one another.
The significance of this discovery is multi-faceted. To begin with, the cycles can be used to identify undetected murders. When an interval between homicides is longer than expected, given its position in the pattern, it likely means a case is missing from the data. All data is plotted based on when the assaultive incident occurred, not when the death or discovery occurs.
Secondly, this information can be used to predict when the new homicides might occur. Currently, the quality of available data and precision of measurements is a major limitation in the study’s predictive clarity. Much work stills needs to be done to better understand how to overcome these hurdles. Earlier work by researchers in Philadelphia discovered that there is a 33% chance of a repeat shooting (not necessarily a homicide) within two weeks and one city block of the previous shooting. We can now apply this logic to homicide and see why it is true.
The most significant importance of this discovery however is what this means for homicide prevention overall. It demonstrates that although individual actors interact and make individual choices, they are still greatly impacted by the larger social structure. As Marcus Felson, a social theorist, and Terance Miethe, a homicide researcher, have predicted, when and where a violent lethal event occurs is predominantly determined by the environment in which it occurs.