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Volume 27, Issue 1, 2006

1st Visible Path Award Winner – Nathaniel Bulkley, 2-3
Vancouver Symposium on sex, drugs, and social networks, 4-7
"Big Events" and Networks, 9-14
Friedman, Samuel, Rossi, Diana, Flom, Peter L.
Some, but not all, "big events" such as wars, revolutions, socioeconomic transitions, economic collapses, and ecological disasters in recent years seem to lead to large-scale HIV outbreaks (Friedman et al, in press; Hankins et al 2002). This was true of transitions in the USSR, South Africa and Indonesia, for example, but not those in the Philippines or (so far) in Argentina. It has been hypothesized that whether or not HIV outbreaks occur is shaped in part by the nature and extent of changes in the numbers of voluntary or involuntary risk-takers, which itself may be related to the growth of roles such as sex-sellers or drug sellers; the riskiness of the behaviors engaged in by risk-takers; and changes in sexual and injection networks and other "mixing patterns" variables. Each of these potential causal processes, in turn, is shaped by the nature of pre-existing social networks and the patterns and content of normative regulation and communication that happen within these social networks-and on how these social networks and their characteristics are changed by the "big event" in question. We will present ideas about what research is needed to help understand these events and to help guide both indigenous community-based efforts to prevent HIV outbreaks and also to guide those who organize external intervention efforts and aid.
Gender and Chain Reactions in Teenagers' Social Networks, 15-23
Kirke, Deirdre M.
Over the past ten years or so there has been renewed research interest in the relative impact of peer selection and peer influence on the increasing similarity of teenagers in their substance use. Researchers have concluded that either peer selection or peer influence explained the similarity. This paper examines this research question differently using complete network data and arrives at different conclusions. Findings emonstrate that similarity in the substance use of teenagers and their peers is explained by either peer selection or peer influence for some, by both peer selection and peer influence for others, and by neither for others. Using a sociological approach and a social network perspective this paper demonstrates how chain reactions result in similarity in the substance use of teenagers in their peer groups, by drawing together those who are similar with those who are not. The paper demonstrates how chain reactions involve peer selection, the patterning of peer ties and peer influence, and explores how gender affects all aspects of the chain reaction process.
The Effect of Personal Network Exposure on Injecting Equipment Sharing among IDUs in Budapest, Hungary, 25-38
Gyarmathy, V. Anna
Until the mid-1990s, the prevalence and incidence of HIV infection was uniformly low in countries across the Central and Eastern European region. In the past decade, however, this has changed dramatically, with a rapid increase in HIV infections in the region, especially in Eastern Europe where 41% of new HIV infection cases were among injecting drug users (IDUs) and as much as 66% of IDUs are infected with HIV in certain regions. While Russia, the largest country in Eastern Europe, has the fastest growing HIV rates in the world, the situation is different in Central Europe. For example, Hungary has low levels of HIV infection – estimated less than 1% of IDUs. Understanding the role of network factors in the spread and prevention of HIV could not only enable us to keep the HIV rates low among IDUs in countries like Hungary, but also provide a means for the effective prevention of other blood-borne and sexually transmitted infections (STIs) that share similar routes of transmission as HIV. Rogers’ diffusion of innovations theory may help explain why HIV rates among IDUs are low in Hungary. Valente’s related exposure or contagion model postulates that the more individuals within a social network adopt an innovation or a practice, the greater the probability of an individual is to adopt this innovation or practice. Personal network exposure (PNE), measured both within egocentric and sociocentric networks quantifies the extent to which a person is exposed to risk through their social network. The aim of this analysis was to assess the association of PNE and other correlates with injecting equipment sharing among IDUs in Budapest, Hungary.
Social Networks and Mathematical Modeling, 39-45
Stanley, Ann
Over the past 30 years, mathematical models of the spread of epidemics and the dynamics of societal cooperation have gradually incorporated more and more information about social network structures. This information is important not just to improve the accuracy of models, but also to improve their qualitative behavior and provide an ever deeper understanding of the spread of diseases and the ways in which individuals interact. Some important questions probably cannot be answered without the use of stochastic simulations that account for the social networks of individual agents.
Homophily and assimilation among sportactive adolescent substance users, 47-63
Pearson, Michael, Steglich, Christian, Snijders, Tom
We analyse the co-evolution of social networks and substance use behaviour of adolescents and address the problem of separating the effects of homophily and assimilation. Adolescents who prefer friends with the same substance-use behaviour exhibit the homophily principle. Adolescents who adapt their substance use behaviour to match that of their friends display the assimilation principle. We use the Siena software to illustrate the co-evolution of friendship networks, smoking, cannabis use and drinking among sport-active teenagers. Results indicate strong network selection effects occurring with a preference for same sex reciprocated relationships in closed networks. Assimilation occurs among cannabis and alcohol but not tobacco users. Homophily prevails among tobacco and alcohol users. Cannabis use influences smoking behavior positively (i.e., increasing cannabis increases smoking). Weaker effects include drinkers smoking more and cannabis users drinking more. Homophily and assimilation are not significant mechanisms with regard to sporting activity for any substance. There is, however, a significant reduction of sporting activity among smokers. Also, girls engaged in less sport than boys. Some recommendations for health promotion programmes are made.
A 45-year Retrospective on Doing Networks, 65-90
Laumann, Edward O.

Volume 27, Issue 2, 2007

Calendar, 1-2
Ties & Bonds, 3-9
Wellman, Barry
The Blog Network in America: Blogs as Indicators of Relationships among US Cities, 15-23
Lin, Jia, Halavais, Alexander, Zhang, Bin
An analysis of links among U.S. weblogs is done to examine the interpersonal social network and social connections among U.S. cities. Drawing 4,241 weblogs from the NITLE census dataset that are identified as being located in the United States, this project extracts the outward links of these weblogs and uses them to analyze the relationship between cities. A total of 632 U.S. city/region units, represented by the first three-digits of US postal codes, are taken as nodes of the network. In total, 41,212 permanent links from blogs of each of the city units are counted as weighted arcs in the network. Inlinks and outlinks of each city unit are recorded for analysis. The study finds that the city units whose bloggers attract most inlinks are Manhattan, San Francisco and Bay Area, Washington, D.C. and its western suburbs, Boston and its suburbs, Los Angeles and Seattle. The study discovers a super-metropolitan cluster, transcending geographical boundaries, within which the cities traditionally associated with cultural elites are closely connected. For other less metropolitan areas, blogs are most heavily connected at a geographically local level, and then extend to a national network.
Modeling Indegree Centralization in NetSAS: A SAS Macro Enabling Exponential Random Graph Models, 25-37
Johnston, M. Francis, Chenb, Xiao, Swigert, Silvia
The dual purpose of this paper is to (1) introduce SAS computer code (NetSAS) facilitating ERGM analysis of network data and (2) empirically investigate estimation and interpretation of the parameter for indegree centralization. NetSAS directly transforms square-matrix network data into rectangular-matrix dyadic data, thereby eliminating the need for computations exogenous to SAS and extensive data management. The macro is illustrated through estimation on 7 graphs of 21 nodes that vary from 0 to 100% on the conventional graph theoretic measure of indegree centralization. ERGM in a conventional statistical package may facilitate wider use of and further dialogue about the meaning, interpretation, and advancement of the ERGM framework.
Measuring tie-strength in virtual social networks, 39-52
Petróczi, Andrea, Nepusz, Tamás, Bazsó, Fülöp
Tie-strength has been in the focus of social science research for decades, yet the use of measurement tools or scales has been relatively scarce. The aim of this study was to fill the gap and provide a tool that is able to provide a quantitative and continuous measure of tie strength in social networks. The focus was on virtual communities because the fast expansion of Internet use and the constant growth of on-line communities provide today’s researchers with an excellent opportunity for effective and speedy data collection regarding tie-strength measures in these virtual social groups. The Virtual Tie-Strength Scale (VTS-Scale) consist of 11 questions and it was developed on a sample of 56 people (3080 asymmetric ties) and tested for reliability of smaller sample of 16 (204 asymmetric ties) independent sample participation regularly on a Hungarian discussion board like forum. Reliability coefficients were reassuringly high for both samples, Cronbach alphas of 0.92 and 0.86, respectively. Data triangulation offered evidence for scale validity. In summary, the VTS-Scale and its scoring method seem to provide a valid and reliable measure of tie strength in virtual communities. Although the aim of the research was to develop a tool that measures tie-strength in virtual communities, the tool can be easily modified for off-line social groups. The VTS-Scale is also capable of distinguishing between two components of tie-strength: acquaintances and friendship. However, the content of each component needs further investigation.
Another Hundred Days: Social Contacts in a Senior Class, 53-58
Portnova, Aleksandra, Lock, Patti Frazer, Ladd, Brian C., Zimmerman, Christine
the graph statistics of the social network resulting from that data. We also use demographic data tracked on a per student basis to examine how acquaintanceship circles differ between different groups. We look explicitly at males/females, students of color, varsity athletes, the effect of different academic majors, transfer students, and members of fraternities/sororities.
Effects of Network Segregation in Intergroup Conflict: An Experimental Analysis, 59-76
Takács,Károly,
Dense in-group and scarce out-group relations (network segregation) often support the emergence of conflicts between groups. A key underlying mechanism is social control that helps to overcome the collective action problem within groups, but contributes to harmful conflicts among them in segregated settings. In this study, a new experimental design is introduced to test whether internalized social control affects contribution decisions in intergroup related collective action. Subjects played single-shot Intergroup Public Good games in two groups of five without communication. Subjects were connected via computers and connection patterns were manipulated to detect forms of social control that are activated conditional on expectations and on the composition of the artificially created ego-network. Results confirm the influence of behavioral confirmation and the conditional impact of internalized selective incentives. As an aggregated consequence of these social control effects, harmful intergroup outcomes were least likely when members of the groups were arranged in a mixed network.

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