Social Networks and Organizational Dynamics

In this paper we develop and test a theory of the dynamic behavior of voluntary groups. The theory combines an image of social network structure with the concept of natural selection to model changes in group composition over time. We consider the group to be a population of members subject to natural selection in sociodemographic space. According to the theory, the probability that members will enter or leave the group depends upon the number and strength of social network ties that connect group members to each other and to nonmembers. We analyze an event history dataset constructedfrom interviews using the Life History Calendar method and information on ego-centered social networks developedfrom the General Social Survey Network Module. We test the hypothesis that network connections inside a group are associated with reduced membership turnover, while connections outside the group increase turnover. We find that weak ties and network connections that span greater distances in sociodemographic space are positively correlated with leaving current groups and joining new ones. We conclude that weak ties are a major source of change in group composition.