Obesity, politics, STDs flow in social networks
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STORY HIGHLIGHTS
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"Connected," a new book, describes social network research -- online and off
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People influence each other within three degrees of separation
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Author: Online social networking is here to stay
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Anthropologist: The expected size of social groups in humans should be about 150
(CNN) -- Meet "network man." He has basic desires of his own, but has many arbitrary preferences, such as in music
or clothes, that have been influenced by the people he knows.
Network man's likes and dislikes, in turn, affect the behavior of his friends, and their friends, and their friends. For
example, when he gets into an obscure indie rock band, he shares an album with his friend, who likes it so much that
he recommends it to his cousin, who spreads the word to her friends.
This is the view of human behavior put forth in "Connected," a new book by Dr. Nicholas Christakis, professor at
Harvard University, and James Fowler, associate professor at the University of California, San Diego.
Examining years of research of their own and from others, the authors conclude that social networks, both offline and
online, are crucial in understanding everything from voting patterns to the spread of disease.
People have profound influences on each other's behavior within three degrees of separation, the authors find. That
means that your friends, your friends' friends, and your friends' friends' friends may all affect your eating habits, voting
preferences, happiness, and more. At the fourth degree, however, the influence substantially weakens.
These are not small effects. "If a mutual friend becomes obese, it nearly triples a person's risk of becoming obese,"
the book said. Even geography doesn't matter; you're still at risk for gaining weight if a friend 1,000 miles away gets
bigger.
Why is that? Obesity seems to spread in networks because of behavioral imitation -- you copy what people close to
you are doing -- and shared expectations called "norms," the authors said. When you see people close to you gaining
weight, that makes you readjust your own idea of what is an acceptable body size.
Still, this does not mean you should get rid of your overweight friends, Fowler said. In fact, the researchers reexamined the same data set and found that people who dumped their friends who gained weight were even more
susceptible to obesity.
"On the one hand, yes, our work showed that if you keep your friend, you are going to be susceptible to their bad
behaviors," he said. "On the other hand, time and again, what our work shows is that every friend makes you
healthier and happier."
Finding the hubs of social networks can be invaluable from a public health point of view, the authors say. For
example, instead of vaccinating everyone in a population against a disease, it may be just as effective to choose
people at random and ask them to name their closest friends, then vaccinate those friends.
The idea is that if someone names you as a friend, you are likely to be more central to the network than a participant
chosen at random. That means you're probably less socially isolated, and more likely to come into contact with a lot
of people, than someone randomly selected.
"You can achieve the same level of protection for the population at one-third the cost doing an intervention like this,"
Fowler said.
In fact, the authors hope to do a preliminary experiment monitoring the spread of the novel H1N1 virus on a college
campus, Fowler said. Using the "friend" method for the vaccine against that virus, distributed for the first time this
week, would not be a bad idea, although it is still a new concept that needs to be tested, Fowler said.
"What you are seeing is a lot of people who are experimenting with these ideas in trials, and trying to figure out how
can we use all of this great new information about social networks to make everybody's life better," he said.
Social networks were crucial to understanding how sexually transmitted diseases broke out among teenagers in 1996
in Rockdale County, Georgia, a quiet upper-middle-class suburb near Atlanta.
An investigation found that a collection of young girls, mostly under 16, had been having sex with various clusters of
boys, the book said. This epidemic of syphillis and other diseases stopped when the network changed, the authors
argue.
"They actually figured out a good intervention there, which was to break apart this central group of girls that were
essentially promoting the spread of this norm of a heightened sexuality at a very young age," Fowler said. "By
essentially quarantining them, the norm couldn't spread anymore, and pretty soon they were able to get control of the
epidemic."
It turns out online social networks haven't necessarily expanded the number of friends the average person has.
Christakis and Fowler looked at all of the Facebook pages of students at a particular unnamed university and tried to
figure out who was close friends with whom based on "picture friends." Their reasoning: Two people who post and
"tag" each other in photos on Facebook are likely to be more socially close than those who do not.
They found that, on average, students had between six and seven close friends on Facebook, which is not far from
sociologists' estimate that most people have four to six close friends in real life.
Moreover, the expected size of social groups in humans, based on their large brain size and the behavior of other
primates, should be about 150, according to British anthropologist Robin Dunbar. At the time "Connected" was
finalized, the average Facebook user had 110 registered friends on the site, Fowler said.
The "Three Degrees Rule" may have evolved with the human species, the authors argue. Having a social network in
which influence spreads is useful, as is knowing who is a potential ally or enemy based on friends' associations. But
humans evolved in small groups, not large collectives, so during early human history there may not have been people
who were four degrees removed from anyone, they write.
The Iranian blogosphere, despite having a government that blocks access to several Web sites, expresses many
viewpoints on the Internet. In June, Iranian citizens used Twitter to organize and protest against what they viewed as
an unfair election.
"In closed societies, the sheer value of being able to spread information quickly is going to be the reason why social
networks play such a strong role," Fowler said.
An important caveat is that political organizing through social networks, just like choosing financial investments,
depends on what you believe other people believe, he said. Bubbles in the stock market. for example, are created
when a lot of people believe a lot of other people highly value a company's stock.
"The same thing happens with these protests," he said. "You're kind of afraid to go out and do it yourself, but if you
think that other people are going to go show up, then you're more likely to show up yourself."
While social networking sites such as Friendster have risen and fallen, online social networking in general is here to
stay, Fowler said. He likened it to the introduction of the telephone, which had its initial skeptics too.
"This is just yet another way through which humans exert their inherent natural tendency to try to connect to other
people that they care about," he said.