Can big data help us predict where crime will strike?

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1. Forecasting crime

In 2011, police in Los Angeles and Manchester ran radical trials. They used a computer algorithm to try to predict where crime would occur before it happened.

That might sound like science fiction, but the police wanted to test if by analysing large amounts of crime data, also known as 'big data', they could spot patterns in the way criminals behaved. Then they'd deploy their resources in the areas the computer predicted crime would strike.

Policing to prevent crime is nothing new. In Britain, it goes back hundreds of years. But if using big data worked, it would mean humans taking advice on where to police from a machine rather than relying on their own experience.

2. How computers predict crime

Patterns in crime data mimic the spread of disease and earthquake aftershocks. Click through the images below to see how predictive policing works.

The following is a hypothetical case study, based on patterns found in crime data by researchers at University College London. A crime occurs at a location, e.g. a house is burgled in a suburb.

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The risk of more burglaries spreads to the surrounding area. It diffuses out from the point of the original crime, with the greatest level of risk within about 200m. The risk is often greater on the same side of the street that the burglary occurred.

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The risk of further crime is greatest within two weeks of the burglary and decreases as time passes. Police may deploy additional resources to the area, e.g. to alert residents and increase patrols. But in our example, another burglary occurs nearby.

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Risk now spreads out from the new burglary and the previous crime, being highest where both areas of risk intersect. Police can focus resources here, and may even share information with other emergency services to increase guardianship in the area.

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3. Does it work?

The 2011 trial in LA was a success, with a significant fall in property crime and burglaries. The LAPD Foothill Division has continued to use predictive software.

UK trials

Trials have taken place across the UK, from Kent to Yorkshire. The results suggest that predictive policing models can help cut crimes where perpetrators exhibit predictable patterns of behaviour. In 2011, for example, in Trafford, Manchester, police noted a 26.6% fall in burglaries, compared to a 9.8% fall across Greater Manchester in the same period.

However, Kent Police had a slightly less straightforward experience. It ran a successful four-month trial starting in December 2012, but after rolling out predictive policing across the county in April 2013, recorded an increase in crime for the following year. It blamed the rise on a failure to deploy resources effectively and inaccurate crime data.

Rachel Tuffin, director of research at the College of Policing, says there is a strong interest in the potential of predictive policing, but further trials are needed. She explains: "Research shows predictive analysis can identify hotspots more accurately, and separate studies show targeting police patrol and problem-solving in hotspots can reduce crime. Forces in the UK and US are testing the effect of combining prediction with action to remove the causes of crime."

4. Ethical dilemmas

Predictive policing promises a new era of law enforcement. But some critics are concerned it may lead to an erosion of civil liberties.

Victimisation

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Victimisation

Critics say it may exacerbate unnecessary stop and searches in areas with high crime rates. Advocates argue it makes police decision-making less biased.

Displacement

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Displacement

Some critics are concerned these methods simply move crime elsewhere, though research at University College London in 2011 found no evidence for this.

Privacy

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Privacy

Civil liberties campaigners argue if predictive policing works, authorities may try to gather further types of sensitive data, leading to invasions of privacy.

Ignores causes of crime

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Ignores causes of crime

Critics worry authorities may neglect the social, economic and cultural factors that cause crime. Advocates argue that a variety of approaches are necessary.