MAKING BETTER CITIZENS:

Set up by David Cameron in 2010 to try to improve public services and save money, the nudge unit still gets most of its work from government, though it has expanded to take on a wider range of projects, including work for foreign governments, the World Bank and the UN. "Essentially we respond to the priorities of government," said Halpern, explaining how the unit chooses its projects. "The key point is that it has to be social purpose."

The team would refuse to help a major drinks company improve sales, for example, but might help with a project to reduce sugar consumption.

Most of the changes applied by the nudge unit are tiny: a text message, rewording a letter, a personalised email. One of Halpern's favourite projects was on improving police diversity. Although around 60% of applicants from a white British background were passing the situational judgment capability stage of Avon and Somerset constabulary's recruitment process, only 40% of black and minority ethnic (BME) applicants passed it. Halpern's team reworded the email sent to all candidates that congratulated them on passing the previous stage to include a request for them to "take some time to think about why you want to be a police constable" before moving on to the next test.

This change had no impact on white applicants' performance in the next stage, but 50% more BME candidates passed after the email was adjusted. Some BME candidates could previously have been trying to respond to the test in a way they thought a white applicant would, said Simon Ruda, the team's head of home affairs - but the new email encouraged them to trust their gut instincts.

Reducing fraud and debt is one of the team's longest-running and most successful projects; the unit previously claimed to have nudged forward the payment of £30m a year in income tax by introducing new reminder letters that informed recipients that most of their neighbours had already paid.

But these letters had little impact on the 1% to 5% of people who owed the most tax. Interestingly, the team has discovered the message that works best for this group: "Not paying tax means we all lose out on vital public services like the NHS, roads and schools". This could be because because their money could credibly make a big difference to these services, the report says.

A similar project in Guatemala was also successful, despite the country's deeply entrenched tendency towards tax avoidance and mistrust of its government. Letters sent by the nudge unit more than tripled tax receipts.

Many nudge techniques play on reciprocity and a personal touch. Another project cut the high dropout rate on government-subsidised adult literacy classes by 36%, simply by sending students a personalised text message every Sunday night that read: "I hope you had a good break, we look forward to seeing you next week. Remember to plan how you will get to your class. Manchester College."

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