In an additional study, we worked with the German Red Cross, which sent information to over 16,000 people who had not donated blood for over two years. They were either thanked for their previous donation, thanked and told how their blood was used, or thanked and told how their next donation would be used. These former blood donors were 11% more likely to donate again when they were told how their blood was used in the past compared to those who were just thanked or told how their future donation could be used.