Researchers at the Keck School of Medicine of the University of Southern California (USC) have developed a new measure that identifies "bridging individuals" in social networks. These individuals act as critical connectors, facilitating the flow of information or spread of diseases between social networks and communities.
The new measure will enable researchers, policymakers and public health professionals to better understand how information or behaviors move from group to group, says Thomas Valente, professor and director of the Master of Public Health program at the Keck School of Medicine of USC, and the principal investigator of the study.
The paper, "Bridging: Locating Critical Connectors in a Network," is available online and will appear in an upcoming issue of the journal Social Networks.
"Past research has focused on identifying central individuals, or leaders, in the group to accelerate behavior change or stem disease spread within groups, organizations or communities," Valente says. "This study shows that identifying bridging individuals who connect two otherwise disconnected subgroups is a more efficient way to achieve these same goals."
While central individuals or opinion leaders in the group are more inclined to maintain the status quo, bridging individuals may be more open to new ideas and practices. Central individuals may also have less capacity to persuade any one individual in the group because they must spread their persuasive energies across many people.
"These bridging individuals appear to be more effective at changing others, and more open to change themselves, which makes them intrinsically interesting to study," Valente says.
In order to calculate an individual's bridging, the team systematically deleted each link in the network and calculated the resulting changes in network cohesion. The average change for each person's links is a measure of bridging. A person with two links to members in two different groups when no one else links the groups is a perfect bridge.
The findings may have particular significance for disease prevention, Valente notes.
"To prevent diseases from spreading within communities, researchers and public health experts usually advocate immunizing central individuals, as they have the greatest effect on preventing further spread. To prevent disease from spreading between communities, however, bridging individuals should be immunized," he says.
The study cites two examples of previous research: A 2005 study that collected friendship data from Dublin adolescents to investigate social network influences on substance use behavior, and data collected among the first 40 HIV cases diagnosed in the U.S. In both cases, the USC researchers' analysis correctly identified the bridging individual who facilitated the spread of the behavior or disease to a different subgroup.
Using the new model may help experts in the future to identify potential bridging individuals and intervene in harmful behaviors, Valente says.
"From a local perspective it makes sense to focus on central individuals. But from a global or macro perspective, bridging is critical," he says.
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