Giving gifts to groups: How altruism depends on the number of recipients

When a single gift goes to a group of recipients, how does giving depend on the size of the group? This question is important for understanding charitable giving and fund-raising, public goods provision, family altruism, and more. If we think of the gift as giving up a dollar to create a social surplus, then we want to know how the number of recipients of that surplus affects its value to the giver. In other words, how congestible is altruism? This paper builds a theoretical framework for this question and begins to answer it with a controlled experiment. The finding is that for most subjects altruism is congestible. For the average subject, a gift that results in one person receiving x is equivalent to one in which n people receive x / n0.68 each.