PredPol Places, a US company, has developed] one of a range of tools using better data, more finely crunched, to predict crime. They seem to promise better law-enforcement. But they also bring worries about privacy, and of justice systems run by machines not people.  Criminal offences, like infectious disease, form patterns in time and space….

Cops working with predictive systems respond to call-outs as usual, but when they are free they return to the spots which the computer suggests. Officers may talk to locals or report problems, like broken lights or unsecured properties, that could encourage crime. Within six months of introducing predictive techniques in the Foothill area of Los Angeles, in late 2011, property crimes had fallen 12% compared with the previous year; in neighbouring districts they rose 0.5%…

For now, the predictive approach works best against burglary and thefts of vehicles or their contents. These common crimes provide plenty of historical data to chew on. But adding extra types of information, such as details of road networks, can fine-tune forecasts further. Offenders like places where vulnerable targets are simple to spot, access is easy and getaways speedy, says Shane Johnson, a criminologist at University College London. Systems devised by IBM, a technology firm, watch how big local events, proximity to payday and the weather affect the frequency and location of lawbreaking. “Muggers don’t like getting wet,” says Ron Fellows, IBM’s expert.

Predicting and forestalling crime does not solve its root causes. Positioning police in hotspots discourages opportunistic wrongdoing, but may encourage other criminals to move to less likely areas. And while data-crunching may make it easier to identify high-risk offenders—about half of American states use some form of statistical analysis to decide when to parole prisoners—there is little that it can do to change their motivation.

Misuse and overuse of data can amplify biases….But mathematical models might make policing more equitable by curbing prejudice…

This sort of transparency about what goes on in predictive systems, and what their assumptions are, may also be a partial solution to worries voiced by Andrew Ferguson, a law professor in Washington, DC. Mr Ferguson fears that judges and juries could come to place too much credence in the accuracy of crime prediction tools, jeopardising justice.

The legal limits on using social media to fish out likely wrongdoers, or create files on them, are contested. Most laws governing police investigations pre-date social networking, and some forces assert that all information posted to public forums is fair game. But Jamie Bartlett of Demos, a British think-tank, says citizens and police forces need clearer guidance about how to map physical-world privacy rights onto online spaces. He thinks gathering information about how someone behaves on social sites ought to require the same clearance needed to monitor them doggedly in public places. Officers who register anonymously or pseudonymously to read content, or send web crawlers to trawl sites against their owner’s wishes, would require yet more supervision.

Identifying true villains among the oddballs and loudmouths found by social-media searches is tricky. Most police efforts are embryonic. Evgeny Morozov, an academic and technology writer, thinks the privacy-conscious have more to fear from crime detection algorithms cooked up by social networks themselves. Some of those firms already alert investigators when they suspect users of soliciting minors. Unlike the cops they employ clever coders who can process private messages and other data that police may access only with a court order.

These projects make life difficult for many criminals. But smart ones use the internet to make predictions of their own. Nearly 80% of previously arrested burglars surveyed in 2011 by Friedland, a security firm, said information drawn from social media helps thieves plan coups. Status updates and photographs generate handy lists of tempting properties with absent owners. It does not take a crystal ball to work out what comes next.

Predictive policing: Don’t even think about it, Economist,July 20, 2013, at 24