a test
of psychological theories of intrinsic motivation (for example, Frey, 1997) or of self-signaling
(Benabou and Tirole, 2006). Furthermore, in one treatment, we send an appeal with the identical
message as in the incentive treatments, but do not oer a reward. This allows us to examine
whether information conveyed through the mailing alone aects blood donations (possibly about
the behavior of others, as stressed in Sliwka (2007))