Behavioural Insights Team boosted organ donor sign-ups with a reciprocity question

By the early 2010s, the UK's organ donor shortfall was severe and growing: roughly 80 percent of adults told surveys they supported organ donation, but only around 40 percent had actually joined the NHS Organ Donor Register, and an average of three people were dying every day for want of a matching donor. The government's own online prompt to register, shown to millions of people renewing their vehicle tax or driving licence on GOV.UK, had been running with a generic civic-appeal message for years with no way to know whether a different message would perform any better.

Guessing at a better message and simply swapping it in risked making things worse with no way to know until well after the fact, and internal debate over which value, social proof, loss aversion, altruism, would motivate people most was exactly the kind of argument that never resolves without a real test against real behavior.

Ran eight distinct framings simultaneously on real traffic, letting actual registration behavior settle the debate; reciprocity won with a 38% relative increase.

Testing eight framings simultaneously on real traffic gave a direct comparison of actual behavior.

The reciprocity question outperformed because it made the ask personal and reciprocal.

Running at national scale meant the result was statistically robust and immediately actionable.

When a persuasive message plateaus, run competing framings live at scale and let behavior decide instead of debating internally.

Across 1,085,322 site visitors, the reciprocity message produced 4,256 registrations versus 3,085 under the control message, an odds ratio of 1.38 and roughly a 38 percent relative increase, outperforming every other framing tested including social-norm and values-based appeals. Scaled to the full annual volume of GOV.UK transactions, the team projected the winning message would add approximately 96,000 additional organ donor registrations a year over the previous default wording.