• 7 minute read

The Power of Social Networks

How face-to-face social networks in which we are embedded affect our lives, and how we could take advantage of these powerful networks to change the world

By Tong Dandan, PhD student, Department of Marketing and Deng Sijing, PhD student, Department of Decision Sciences and Managerial Economics

“Human beings are embedded in complex webs of social networks. These networks obey particular biological, physiological, sociological and mathematical rules,” said Professor Nicholas A. Christakis, the Sol Goldman Family Professor of Social and Nature Science at Yale University, during his seminars at the Chinese University of Hong Kong in September 2016. The seminars were organized by the CUHK Business School’s Department of Marketing.

“Understanding those rules gives us new ways to understand human behaviors and new ways to intervene those behaviors to make the world a better place,” he said.

A leading expert on social network science, Prof. Christakis was named to the 2009 TIME 100 and also the 100 Top Global Thinkers by Foreign Policy in both 2009 and 2010. He directs Yale University’s Human Nature Lab, which focused on the relationship between social networks and human well-being.

Using both observational and experimental methods, his research published in top-notch journals including Nature and The Lancet, engages two types of phenomena: the social, mathematical, and biological rules governing how social networks form (‘connection’), and the biological and social implications of how they operate to influence people’s thoughts, feelings, and behaviors (‘contagion’).

During his lectures at CUHK, Prof. Christakis reviewed his research on social networks over the past 15 years, shedding light on some of the key issues in the field.

How We Form Social Networks

According to Prof. Christakis, our friendship with a person is partially determined by our genes.

“46 percent of the variation in how many friends you have is explained by your genes. And this is not surprising, as we know that some people are born shy and some gregarious. But we also found that 47 percent of the variation in whether our friends know each other is attributable to our genes. The reason is that people show different inclinations to introduce their friends to each other,” he said.

“Some people like to introduce their friends to each other, and others keep them apart and don’t introduce their friends to each other. And so some people knit together the networks around them, creating a kind of dense web of ties in which they’re comfortably embedded,” Prof. Christakis added.

Moreover, his team found that 30 percent of the variation in whether or not people are in the middle or on the edge of the network can also be attributed to their genes.

“In other words, our genes can determine how many friends we have, and how our friends are connected to each other.”

“Policy makers can intervene a social network by changing its structure. They can target influential individuals in a social network rather than random individuals, as an effort to magnify the effects of their interventions.” – Prof. Nicholas A. Christakis

Three Degrees of Influence

When it comes to the influence of social networks, Prof. Christakis’s research has shown that it obeys a rule called “Three Degrees of Influence”, which means that everything we do tends to ripple and flow through our social network, having an impact on our friends (one degree), our friends’ friends (two degrees), and then our friends’ friends’ friends (three degrees).

In other words, behaviors of the friends of your friends’ friends can predict your behavior.

For example, obesity can be contagious, according to his study.

“If your friends are obese, your risk of obesity is 45 percent higher. And if your friend’s friends are obese, your risk of obesity is 25 percent higher. And then if your friend’s friend’s friend, someone you probably don’t even know, is obese, your risk of obesity is still 10 percent higher,” he said.

“It’s only when you get to your friend’s friend’s friend’s friends that there’s no longer a relationship between that person’s body size and your own body size,” he said.

As a matter of fact, the principle of “Three Degrees of Influence” applies broadly in social phenomenon of obesity, smoking, drinking, drug use, happiness, loneliness, depression, altruism, crime, voting, purchasing, and ideas diffusion, the professor pointed out. So what is the mechanism behind it? According to Prof. Christakis, there are at least three reasons for such phenomenon.

“One possibility is a kind of induction or spread from person to person, like my weight gain is causing your weight gain. For example, your friends say to you: “Let’s go have muffins and beer”. You follow along and start gaining weight like them. Another more subtle possibility is that they start gaining weight, and it changes your idea of what an acceptable body size is. What’s spreading from person to person is not a behavior, but rather a norm: An idea is spreading.”

“Another reason is that the similarity of body size makes people tie together, which is called homophily, or birds of a feather flock together. The third reason is what is known as confounding, because it confounds our ability to figure out what’s going on, or the common exposure we share, like a health club that makes us both lose weight at the same time.”

Implications on Policy Making

Prof. Christakis believes that social network science has the potential to be used for improving the society and human well-being, a belief which he has been obsessed with for over 15 years.

“We have been wondering whether it might be possible to take advantage of the insight [we found in our research about social networks], to actually find ways to improve the world, to actually fix things, and not just understand things. One of the first things we thought we would tackle is how to go about predicting epidemics,” said Prof. Christakis.

He and his research team tested the idea with an outbreak of H1N1 flu at Harvard College in the fall and winter of 2009. They took 1,300 randomly selected undergraduates and asked them to nominate their friends. And then they followed both the random students and their friends daily in time to see whether or not they had the flu epidemic by looking at whether or not they had gone to university health services. And also, they asked the students and their friends to email them a couple of times a week. In the end, exactly what they predicted happened. By monitoring the friends group, they could get 16 days advance warning of an impending epidemic in this human population.

“By learning about the structure of various networks, we can identify where the hubs are, those who are likely to spread an idea or behavior quickest, and intervene at those points to stop the spread of an unhealthy behavior, or to promote a positive one, or to facilitate the diffusion of innovation or coordination in groups,” Prof. Christakis said.

According to him, there are two broad ways of intervention to improve the world: changing the structure and changing the flow. Changing the structure is the intervention that rewires the connections between people; changing the flow is the intervention that manipulates social contagion, facilitating the flow of desirable properties within groups.

“Policy makers can intervene a social network by changing its structure”, he said. “They can target influential individuals in a social network rather than random individuals, as an effort to magnify the effects of their interventions,” he further suggested.

As shown in one of his field studies, encouraging six central people in a poor village to adopt clean water has proven to be ten times more effective in influencing the whole village than encouraging six random people.

“Both graphite and diamond are made of carbon atoms. But different structure of the carbon atoms connections causes the different properties of graphite and diamond,” said Prof. Christakis. “Similarly, the structure of connections matters in social networks. Grouping people differently can produce different properties in a social network.”

Social Network As Social Capital

In the same way we convert lands into farms and trees into lumber or even to a violin with more effort, social capital is a change in the relations among persons, a change that renders the group more productive and capable of doing things it previously was not able to.

“There is value in these social connections. One of the reasons we human beings make social networks and have done so is precisely to create this kind of social capital.

“By understanding our social networks and how valuable they are, it’s possible for us to improve the society and human well-being,” Prof. Christakis concluded.


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