Collective action. Members of small, concentrated and homogeneous communities or interest groups have more incentives to cooperate and participate in collective action than members of large, dispersed and heterogeneous groups. In the public arena, small groups tend to have relatively more access to public resources at the expense of large groups.
Voice versus exit. Collective action for the advancement of collective interests or "voice" weakens and may fail if the rival action of "exit" in search of an alternative provider is less costly and more likely to give access to public goods.