The challenge
Many people paid their income tax late, creating debt and costly enforcement.
The case
In 2011 and 2012, HM Revenue & Customs and the Behavioural Insights Team ran two trials with more than 200,000 UK taxpayers who had not paid on time. In the first, 101,471 people were randomly sent the standard reminder letter or one with an added sentence, such as 'Nine out of ten people in the UK pay their tax on time', or a message about public services. The social-norm letters increased payment within 23 days, and the strongest added 'You are currently in the very small minority of people who have not paid us yet'. A second trial with 119,527 taxpayers repeated this result. The authors estimate that more than £9 million was collected in its 23 days because of the messages, at practically zero cost.
Why it worked
Specific, true information about what others do changes behavior more than generic appeals. Small per-person effects become large when applied to millions of letters.
Sources
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