Yale research suggests habits spread through connected people.
Highlights:
- Social networks are a kind of web made up of people connected to one another.
- Public health interventions are more effective when they focus on highly connected individuals, who can influence many others around them.
- The structure of social networks matters. The same group of people can produce very different outcomes depending on how they are connected.
- The “friendship paradox” helps identify influential people without mapping an entire community, making large-scale interventions more practical.
- Social contagion can be harnessed as a powerful tool to improve public health, particularly for challenges such as maternal-child health, diabetes, and health education.
For more than a decade, a team from Yale University has worked in communities near the border between Honduras and Guatemala, deep in the rainforest. Their goal has been to determine whether certain individuals within a community can influence the health and behaviors of the broader population. “We have mapped the social networks of 176 isolated communities, encompassing around 30,000 people,” explains Dr. Nicholas Christakis, a physician and sociologist who has devoted his career to studying how behavior spreads.
Your friend may have a greater reach than you when it comes to spreading information.
Ana Karina Raygoza
The Yale Institute for Network Science studies social networks, a kind of web made up of people connected to one another. You know your family, friends, neighbors, and colleagues; they, in turn, know others. Together, these relationships form a network in which dots represent people and lines represent connections. In many cases, “your friend may have a greater reach than you when it comes to spreading information,” explains Dr. Ana Karina Raygoza, a Mexican physician who also works at the Institute and has participated in the fieldwork in Honduras.
The researchers focused on behaviors related to maternal and child health, including breastfeeding, umbilical cord care, and diarrhea prevention. They wanted to see whether healthy practices could spread organically throughout a community. By educating people who occupied more central positions within the network, those with the largest number of social connections, they began to observe how these behaviors became “contagious.”
I took a year away from medical school to complete a master’s degree in public health.
Nicholas Christakis
Much of Dr. Christakis’s career has been shaped by a desire to understand how human connections influence health. His path into this field was driven partly by circumstance and partly by curiosity. One of the main reasons was his mother’s illness while he was studying medicine at Harvard University. “I needed to be more available to help care for her,” he recalls. Pursuing intensive clinical training was difficult because it required constant hospital presence. Being a student attending classes, however, offered more flexibility. “I took a year away from medical school to complete a master’s degree in public health. Through a series of fortunate events, I ultimately decided to pursue a PhD in sociology.” Along the way, he says, he was deeply influenced by Dr. Renée Fox, widely regarded as one of the founders of modern medical sociology.
You take the same atoms and connect them in one way or another, and you get something completely different.
Nicholas Christakis
“Most people learned in high school that there are at least two forms of carbon,” Christakis explains. There is graphite, soft and dark, and there is diamond, hard and transparent. Both are composed entirely of carbon atoms. In graphite, the atoms are linked one way; in diamond, they are arranged differently. “You take the same atoms and connect them in one way or another, and you get something completely different,” he says. The outcome depends not on the carbon atoms themselves, but on how they are connected. At the Institute, researchers have shown that the same principle applies to human beings. You can take a group of people and connect them one way, and they may become happier. Connect them differently, and they may become less happy. Kindness or violence, wealth or poverty, health or illness can emerge from the way individuals are connected to one another.
“I started to see the impact that this educational intervention had in rural populations in Honduras,” Raygoza explains. The team has come to realize that social connections are powerful forces that shape the outcomes of the communities they study. “Social contagion” refers to the process through which behaviors, emotions, and information spread through these connections. Many of today’s challenges are closely tied to this phenomenon. Misinformation, for example, is perhaps one of the clearest cases. False ideas and polarizing narratives spread through networks in much the same way that viruses do. Yet, as Christakis points out, “we can use social contagion to improve outcomes in development economics and public health.”
Understanding how behaviors spread also requires understanding how networks are organized. This is where one of the field’s most fascinating concepts emerges. The friendship paradox helps explain how networks function and why public health interventions based on them can be so effective. The paradox states that “your friends are more central in the social network than you are,” explains Raygoza. It sounds counterintuitive, but it occurs because highly connected individuals are more likely to appear within many people’s social circles. In Honduras, the Institute has used this principle by asking people to identify their friends rather than attempting to map every individual in a community. “We have leveraged it to identify the most popular individuals in a community without needing to map the entire network,” says Christakis.
“What I want to do is use social networks to build public health programs, particularly those focused on diabetes,” Raygoza says, reflecting on how these ideas could be applied to chronic diseases. Her goal is to complete a medical residency in the United States and then apply what she has learned from Dr. Nicholas Christakis to high-impact projects.
He wants people to trust science a little more again.
Ana Karina Raygoza
“It took me years to reach the frontier of scientific knowledge where I could truly see something no one had ever seen before,” Christakis says. Hoping to bring people closer to science once again, he launched the YouTube channel For the Love of Science. The project aims to help more people understand how science works and to push back against the growing wave of irrationality in today’s world. “He wants people to trust science a little more again,” Raygoza explains. In his first video, published four months ago, Christakis speaks about the feeling of discovery, one of the greatest rewards of a scientific career. “It is an intoxicating feeling. It is an extraordinary feeling. I can’t even describe what it feels like,” he concludes.
