Those Outsiders: How Downstream Externalities Affect Public Good Provision

Some policy problems pit the interests of one group against those of another group. One group may, for example, determine the provision of a project (such as a power plant or a dam) that benefits group members but has downstream externalities that hurt people outside the group. We introduce a model of projects with such asymmetries. In-group members may contribute to a common fund that benefits them as a public good. In the model, benefits from the project may or may not vary within the group. Project provision has negative downstream externalities: common fund contributions hurt agents outside the in-group (“Outsiders”) rendering common fund contributions anti-social overall. Many models of social preferences predict that such externalities should reduce or eliminate project provision, although conditional cooperation or a preference for in-group members may counteract this effect. We test this model with a lab experiment. With homogeneous in-group benefits, the presence of negative downstream externalities reduces contribution levels by nearly half. We introduce a rotating high-return position that allows subjects to trade favors. Contributions diminish only slightly with the introduction of the negative externality and reciprocal giving occurs whether or not Outsiders are present.