May 3, 2008

fighting crime with math

Could we cut crime without resort to drama, political posturing, or needless injury and death? Cue mathematics [sub. req.]:
One of the earliest studies using this approach was led by Michael Batty of University College London. Since its inception in 1964, the Notting Hill carnival in London has grown to attract more than a million visitors each year. With vast crowds jammed into narrow streets, crime is inevitable - anything from pickpocketing and shoplifting to violent assault and worse. After three people were murdered at the event in 2000, the Greater London Authority commissioned a review of public safety and asked Batty to create a computer model of people's movements in an attempt to identify better crowd-management strategies. "We simulated the crowd movement around the parade and the exhibits," says Batty, "and used the model to test 'what if' scenarios for changing the parade route, or closing particular streets."

This led to the discovery that altering the parade route could significantly reduce the density of the crowds. "The circular parade route didn't let people easily cross it," says Batty. "This was the problem, as all the events were inside the route." Enlightened carnival organisers adopted the straighter route suggested by the computer analysis, and subsequent carnivals registered a big drop in both maximum crowd densities and the number of crimes committed.

Bowers's finding that burglaries spread like communicable diseases is another example of the power of computer modelling. It first emerged from work with her colleague Shane Johnson, completed four years ago. They studied data from the Merseyside region of the UK, containing information on locations and times of residential burglaries committed over 14 months within an area of about 26 square kilometres. This revealed that, following a given burglary, the likelihood of another was increased for the next two weeks for any house within about 200 metres, though the probability tailed off at greater distances and after that time had elapsed. This pattern of communicability of crime strongly mirrors the patterns that epidemiologists find with diseases that spread from one person to another. In the case of crime, Bowers and Johnson suspect, communicability arises simply because burglars have routines, and after one success they often continue in familiar territory nearby.
Seems a lot smarter than this approach.

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