Empirical evidence suggests that people on average overestimate their own ability in a variety of circumstances. Little is known, however, about the origins of such overconfidence. To shed some light on this issue, we use the classic twin design to estimate the genetic and environmental...

In his seminal 1970 book, The Gift Relationship, Richard Titmuss argued that monetary compensation for donating blood might crowd out the supply of blood donors. To test this claim we carried out a field experiment with three different treatments. In the first treatment subjects were given the...