We rst discuss the potential eects
of the experimental treatments on usable donations, and then turn to rejected donations.
We focus on two types of theories that propose systematically dierent models of interaction
between material incentives and prosocial motivation. First-generation models of prosocial
behavior in economics treat oers of material rewards as selective incentives that generate a standard
relative price eect (see, for example, the review of theoretical contributions on prosocial
motivation in Andreoni (2007)). Material incentives are thus predicted to have a non-negative
eect on the required behavior; that is, on voluntary contributions.