James Moody

Race, School Integration, and Friendship Segregation in America1

Integrated schools may still be substantively segregated if friendships fall within race. Drawing on contact theory, this study tests whether school organization affects friendship segregation in a national sample of adolescent friendship networks. The results show that friendship segregation peaks in moderately heterogeneous schools but declines at the highest heterogeneity levels. As suggested by contact theory, in schools where extracurricular activities are integrated, grades tightly bound friendship, and races mix within tracks, friendship segregation is less pronounced. The generally positive relation between heterogeneity and friendship segregation suggests that integration strategies built on concentrating minorities in large schools may accentuate friendship segregation.

Structural cohesion and embeddedness: A hierarchical concept of social groups

While questions about social cohesion lie at the core of our discipline, no clear definition of cohesion exists. We present a definition of structural cohesion based on network connectivity that leads to an operationalization of a dimension of social embeddedness. Structural cohesion is defined as the minimum number of actors who, if removed from a group, would disconnect the group. This definition leads to hierarchically nested groups, where highly cohesive groups are embedded within less cohesive groups. An algorithm developed and implemented (by Authors) identifies these nested groups by levels of structural cohesion, and thus measures the maximum levels of structural cohesion possessed by individuals as members of structurally cohesive subgroups. We discuss the theoretical implications of this definition and demonstrate the empirical applicability of our conception of nestedness by testing the predicted correlates of our cohesion measure within high school friendship and interlocking directorate networks.

The Structure of a Social Science Collaboration Network: Disciplinary Cohesion from 1963 to 1999:

Has sociology become more socially integrated over the last 30 years? Recent work in the sociology of knowledge demonstrates a direct linkage between social interaction patterns and the structure of ideas, suggesting that scientific collaboration networks affect scientific practice. I test three competing models for sociological collaboration networks and find that a structurally cohesive core that has been growing steadily since the early 1960s characterizes the disciplines coauthorship network. The results show that participation in the sociology collaboration network depends on research specialty and that quantitative work is more likely to be coauthored than non-quantitative work. However, structural embeddedness within the network core given collaboration is largely unrelated to specialty area. This pattern is consistent with a loosely overlapping specialty structure that has potentially integrative implications for theoretical development in sociology.

Chains of Affection: The Structure of Adolescent Romantic and Sexual Networks 1

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.

Dynamic network visualization

Increased interest in longitudinal social networks and the recognition that visualization fosters theoretical insight create a need for dynamic network visualizations, or network “movies.” This article confronts theoretical questions surrounding the temporal representations of social networks and technical questions about how best to link network change to changes in the graphical representation. The authors divide network movies into (1) static flip books, where node position remains constant but edges cumulate over time, and (2) dynamic movies, where nodes move as a function of changes in relations. Flip books are particularly useful in contexts where relations are sparse. For more connected networks, movies are often more appropriate. Three empirical examples demonstrate the advantages of different movie styles. A new software program for creating network movies is discussed in the appendix.

Concurrent Partnerships and HIV Prevalence Disparities by Race: Linking Science and Public Health Practice

Concurrent sexual partnerships may help to explain the disproportionately high prevalence of HIV and other sexually transmitted infections among African Americans. The persistence of such disparities would also require strong assortative mixing by race. We examined descriptive evidence from 4 nationally representative US surveys and found consistent support for both elements of this hypothesis. Using a data-driven network simulation model, we found that the levels of concurrency and assortative mixing observed produced a 2.6-fold racial disparity in the epidemic potential among young African American adults.

Human Resource Management and Organizational Performance

The idea of a transformed or high-performance work system has attracted considerable attention in the United States as an alternative to traditional, mass-production forms of work organization. This article examines the relationships between indicators of high-performance work organizations that are available in the National Organizations Study, on one hand, and measures of organizational performance, on the other. The authors find that characteristics of high-performing work organizations tend to cluster together into a system of organizations. Moreover, the results indicate that human resource policies and practices often identified with high-performing organizations do, in fact, enhance organizational performance.

Peer influence groups : identifying dense clusters in large networks

Sociologists have seen a dramatic increase in the size and availability of social network data. This represents a poverty of riches, however, since many of our analysis techniques cannot handle the resulting large (tens to hundreds of thousands of nodes) networks. In this paper, I provide a method for identifying dense regions within large networks based on a peer influence model. Using software familiar to most sociologists, the method reduces the network to a set of m position variables that can then be used in fast cluster analysis programs. The method is tested against simulated networks with a known small-world structure showing that the underlying clusters can be accurately recovered. I then compare the performance of the procedure with other subgroup detection algorithms on the MacRea and Gagnon prison friendship data and a larger adolescent friendship network, showing that the algorithm replicates other procedures for small networks and outperforms them on the larger friendship network.

The Importance of Relationship Timing for Diffusion

Relationship timing can have dramatic effects on diffusion through a network, as relationship order determines transmission routes. Though past research has modeled diffusion through static networks or developed methods for modeling change in network patterns, none has combined these factors to show how relationship change channels diffusion. This article formalizes the diffusion problem in networks with changing relations, identifies minimal bounds needed to measure diffusion potential in such networks, and provides a method for identifying who is at risk for diffusion. The effect of timing for diffusion potential is demonstrated with potential flow of sexually transmitted diseases (STDs) in an adolescent romantic network.

THE STRUCTURE OF CRITICAL CARE TRANSFER NETWORKS

Rationale:Moving patients from low-performing hospitals to high-performing hospitals may improve patient outcomes. These transfers may be particularly important in critical care, where small relative improvements can yield substantial absolute changes in survival. Objective:To characterize the existing critical care network in terms of the pattern of transfers. Methods:In a retrospective cohort study, the nationwide 2005 Medicare fee-for-service claims were used to identify the interhospital transfer of critically ill patients, defined as instances where patients used critical care services in 2 temporally adjacent hospitalizations. Measurements:We measured the characteristics of the interhospital transfer network and the extent to which intensive care unit patients are referred to each hospital in that network—-a continuous quantitative measure at the hospital-level known as centrality. We evaluated associations between hospital centrality and organizational, medical, surgical, and radiologic capabilities. Results:There were 47,820 transfers of critically ill patients among 3308 hospitals. 4.5% of all critical care stays of any length involved an interhospital critical care transfer. Hospitals transferred out to a mean of 4.4 other hospitals. More central hospital positions were associated with multiple indicators of increased capability. Hospital characteristics explained 40.7% of the variance in hospitals’ centrality. Conclusions:Critical care transfers are common, and traverse an informal but structured network. The centrality of a hospital is associated with increased capability in delivery of services, suggesting that existing transfers generally direct patients toward better resourced hospitals. Studies of this network promise further improvements in patient outcomes and efficiency of care.