As we have developed our understanding of how organizers would use their social networks in mobilizing collective action, we have come to understand the importance of the process we have called “selectivity.” Selectivity is the ability to focus mobilizing efforts on the members of a population who are most likely to contribute or who are likely to contribute the most. Once we assume that collective action usually involves selected members of a population rather than a whole population, we need to develop some systematic theory regarding how processes of selection interact with group characteristics and mobilization strategies. In this chapter, we develop two alternate approaches to modeling the selection process and provide detailed quantitative analysis of the complex interactions they imply. Both models require many simplifying assumptions, so neither is particularly realistic. Nevertheless, each illuminates the dynamics of situations approximated by the model.

Consider the decisions being made by an organizer in the field. If she can afford to contact everyone in her network, she does, and there is no selection involved. But suppose that organizing costs are high and her resources are low. Then she can only contact some fraction of the people she knows and could potentially organize. Whom will she contact? Most often, past theorizing has implicitly assumed that organizers randomly pick targets. This assumption is implicit in the use of the group mean as the estimate for the amount of contribution the organizer can expect to get from each contacted participant – as if she randomly chooses from her network. But random choice would be silly and wasteful.