The B.I.T. worked with a HMRC office (n=1,500) to see whether using social proofcould increase charitable giving among employees. In December 2012 employees of the office received e-cards from HMRC employees who currently donated to charity. The control group received an e-card from an existing donor simply explaining why that person donates and asking the recipient to join them. The treatment group received the same card but with an attached picture of the existing donor. This addition of a picture increased the number of new donors from 2.9% to 6.4%.