Topics in Quantitative Sociology

Fall 2020 ENSAE

Social networks

The development of social network analysis (SNA), in which sociologists play a central role, provides a gateway to the identification of fundamental structural determinants of social behavior. To appreciate the power of SNA, we examine its contribution to the study of job searches.

Background readings

Case-study for reading and commentary

Rajkumar & al., 2022, Sci, "A causal test of the strenght of weak ties"

The authors analyzed data from multiple large-scale randomized experiments on LinkedIn’s People You May Know algorithm, which recommends new connections to LinkedIn members, to test the extent to which weak ties increased job mobility in the world’s largest professional social network. The experiments randomly varied the prevalence of weak ties in the networks of over 20 million people over a 5-year period, during which 2 billion new ties and 600,000 new jobs were created. The results provided experimental causal evidence supporting the strength of weak ties and suggested three revisions to the theory. First, the strength of weak ties was nonlinear. Statistical analysis found an inverted U-shaped relationship between tie strength and job transmission such that weaker ties increased job transmission but only to a point, after which there were diminishing marginal returns to tie weakness. Second, weak ties measured by interaction intensity and the number of mutual connections displayed varying effects. Moderately weak ties (measured by mutual connections) and the weakest ties (measured by interaction intensity) created the most job mobility. Third, the strength of weak ties varied by industry. Whereas weak ties increased job mobility in more digital industries, strong ties increased job mobility in less digital industries.

Case-studies for presentation

This article describes the structure of the adolescent romantic and sexual network in a population of over 800 adolescents residing in a midsized town in the midwestern United States. Precise images and measures of network structure are derived from reports of relationships that occurred over a period of 18 months between 1993 and 1995. The study offers a comparison of the structural characteristics of the observed network to simulated networks conditioned on the distribution of ties; the observed structure reveals networks characterized by longer contact chains and fewer cycles than expected. This article identifies the micromechanisms that generate networks with structural features similar to the observed network. Implications for disease transmission dynamics and social policy are explored.
Nearly a century of empirical research examines how neighborhood properties influence a host of phenomena such as crime, poverty, health, civic engagement, immigration, and economic inequality. Theoretically bundled within these neighborhood effects are institutions’ and actors’ social networks that are the foundation of other neighborhood-level processes such as social control, mobilization, and cultural assimilation. Yet, despite such long-standing theoretical links between neighborhoods and social networks, empirical research rarely considers or measures dimensions of geography and social network mechanisms simultaneously. The present study seeks to fill this gap by analyzing how both geography and social networks influence an important social problem in urban America: gang violence. Using detailed data on fatal and non-fatal shootings, we examine effects of geographic proximity, organizational memory, and additional group processes (e.g., reciprocity, transitivity, and status seeking) on gang violence in Chicago and Boston. Results show adjacency of gang turf and prior conflict between gangs are strong predictors of subsequent gang violence. Furthermore, important network processes, including reciprocity and status seeking, also contribute to observed patterns of gang violence. In fact, we find that these spatial and network processes mediate racial effects, suggesting the primacy of place and the group in generating gang violence.
Personal network change is largely driven by transitions between the groups and organizations where people spend their day-to-day lives. But, how do entrants choose which relationships to pursue among the numerous possibilities a new environment offers? We expect newcomers will use the same mechanisms as longer-tenured members, although this will take time as they acclimate and form initial relationships that support future ties. Thus, our goal is to understand how the network selection processes used by new organizational members shift in importance as time in the organization grows. We focus on network selection via homophily, propinquity, formal relations, and endogenous network processes. For each mechanism, we distinguish between change in the strength of the mechanism and opportunities to enact the mechanism. We evaluate expected changes using network data from a prison-based therapeutic community (TC). This setting is ideal because the structured nature of TC entry and exit generates regular membership turnover and removes confounds present in studies of more familiar contexts (e.g., schools). Results show that the relative importance of network selection mechanisms varies over tenure, with homophily dominating early on and endogenous network processes catching up later. We discuss implications of these findings for new member socialization and broader patterns of inequality.
Most sociological research assumes that social network composition shapes individual beliefs. Network theory and research has not adequately considered that internalized cultural worldviews might affect network composition. Drawing on a synthetic, dual-process theory of culture and two waves of nationally-representative panel data, this article shows that worldviews are strong predictors of changes in network composition among U.S. youth. These effects are robust to the influence of other structural factors, including prior network composition and behavioral homophily. By contrast, there is little evidence that networks play a strong proximate role in shaping worldviews. This suggests that internalized cultural dispositions play an important role in shaping the interpersonal environment and that the dynamic link between culture and social structure needs to be reconsidered.