this paper has been provided by the Social Science and Humanities Research Council of Canada (General and Strategic grants), Bell Canada, the Ontario Ministry of Science and Technology, and the Information Technology Research Centre. We dedicate this chapter to science-fiction personage Judith Merril who net surfed for fifty years until her death in Sept., 1997.

This paper is dedicated to Philip J. Stone III, who first put me online in 1965.

A central idea in marketing and diffusion research is that influentials—a minority of individuals who influence an exceptional number of their peers—are important to the formation of public opinion. Here we examine this idea, which we call the “influentials hypothesis,” using a series of computer simulations of interpersonal influence processes. Under most conditions that we consider, we find that large cascades of influence are driven not by influentials, but by a critical mass of easily influenced individuals. Although our results do not exclude the possibility that influentials can be important, they suggest that the influentials hypothesis requires more careful specification and testing than it has received.

We perform sensitivity analyses to assess the impact of missing data on the structural properties of social networks. The social network is conceived of as being generated by a bipartite graph, in which actors are linked together via multiple interaction contexts or affiliations. We discuss three principal missing data mechanisms: network boundary specification (non-inclusion of actors or affiliations), survey non-response, and censoring by vertex degree (fixed choice design), examining their impact on the scientific collaboration network from the Los Alamos E-print Archive as well as random bipartite graphs. The simulation results show that network boundary specification and fixed choice designs can dramatically alter estimates of network-level statistics. The observed clustering and assortativity coefficients are overestimated via omission of affiliations or fixed choice thereof, and underestimated via actor non-response, which results in inflated measurement error. We also find that social networks with multiple interaction contexts may have certain interesting properties due to the presence of overlapping cliques. In particular, assortativity by degree does not necessarily improve network robustness to random omission of nodes as predicted by current theory.

This paper was originally prepared for presentation to the seminar series on social and institutional change at the Robert Wood Johnson Foundation, Princeton, N.J., organized by Paul DiMaggio. I appreciate the insightful comments of Art Stinchcombe on the earlier draft.

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Abstract: We propose a new class of game-theoretic models for network formation in which strategies are not directly related to edge choices, but instead correspond more generally to the exertion of social effort. This differs from existing models in both formulation and results: the observed social network is a byproduct of a more expressive strategic interaction, which can more naturally explain the emergence of complex social structures. Within this framework, we present a natural network formation game in which agent utilities are locally defined and that, despite its simplicity, nevertheless produces a rich class of equilibria that exhibit structural properties commonly observed in social networks – such as triadic closure – that have proved elusive in most existing models. Specifically, we consider a game in which players organize networking events (or gatherings) at a cost that grows with the number of attendees. A gathering’s cost is assumed by the organizer but the benefit accrues equally to all attendees: a link is formed between any two players who see each other at more than a certain number r0 of gatherings per time period, whether at gatherings organized by themselves or by third parties. The graph of connections so obtained is the social network of the model. We analyze the Nash equilibria of this game for the case in which each player derives a benefit a> 0 from all her neighbors in the social network and when the costs are linear, i.e., when the cost of a

Drawing on the concept of relational embeddedness and the associated mechanisms of mutual understanding, trust, and commitment, we examine how leaders ’ prior exchange experiences influence the likelihood of subsequent interorganizational exchange. We begin to develop a microlevel model of organization-level relations that accounts for nodal multiplexity. In data on baseball player trades, we found that individual leaders ’ ties affected exchanges less than did an organization’s other ties. The sharing of exchange experiences by organizations and their current leaders increased the influences of those experiences on exchange behavior. Thus, leaders have more influence within their organizational contexts than in isolation. For their helpful advice on this project, we thank

This paper assesses the novelty of NSMs- or better, of any social and political movement in contemporary Western societies- in the light of their capacity to develop systems of relationships which cut across established social and political cleavages. It illustrates first the relational bases of Rokkan’s concept of cleavage, and its contribution to the understanding of social movements; it then shows how Simmel’s concept of the intersection of social circles and his distinction between concentric and crosscutting circles may be fruitfully applied to the analysis of political cleavages and their changing forms. In the conclusions, the elements of an approach to the study of the newness of social movements, based on the integration of Rokkan’s and Simmel’s principles, are introduced. 2