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The aftershocks of crime
An idea borrowed from seismology may help to predict criminal activity
The Economist
October 21, 2010
LOS ANGELES is one of the most under-policed cities in America. With a mere 26 officers for every 10,000 residents (Chicago, by comparison, has 46), the Los Angeles Police Department (LAPD) needs all the help it can get.
That help may be at hand, with a modification of technology used to predict another type of threat that the city is prone to: the aftershocks from earthquakes. Big earthquakes are unpredictable. Once they have happened, however, they are usually followed by further tremors, and the pattern of these is tractable.
George Mohler, a mathematician at Santa Clara University, in California, thinks something similar is true of crimes. |
There is often a pattern of “aftercrimes” in the wake of an initial one. The similarity with earthquakes intrigued him and he wondered if the mathematical formulas that seismologists employ to predict aftershocks were applicable to aftercrimes, too.
To test this idea, he and a team of researchers from the University of California, Los Angeles, adapted a computer program used by seismologists to calculate the likelihood of aftershocks. They then seeded it with actual LAPD data on 2,803 residential burglaries that occurred in an 18km-by-18km region of the San Fernando valley, one of the city's largest districts, during 2004. Using the seismological algorithms, the computer calculated which city blocks were likely to experience the highest number of burglaries the next day, and thus which 5% of homes within the area were at particular risk of being broken into. In one test the program accurately identified a high-risk portion of the city in which, had it been adequately patrolled, police could have prevented a quarter of the burglaries that took place in the whole area that day.
In addition to modelling burglary, Dr Mohler examined three gang rivalries in Los Angeles, using data from 1999 to 2002, and discovered that similar patterns emerge from gang violence as retaliations typically occur within days—and metres—of an initial attack. That, too, should help police deploy their limited resources more effectively. RoboCop move over, then. ComputerCop is coming. |
