When it comes to changing health behaviors, it takes more than a far-flung network of friends on Facebook egging you on. It takes a jostling herd, U.S. researchers said Thursday.
Social scientists have assumed that changing behavior would spread like the flu, which transmits best via individuals with lots of long-distance contacts.
But to change behavior, you need to be surrounded by the message — with neighbors, family and members in the community all reinforcing the same idea.
"For about 35 years, wisdom in the social sciences has been that the more long ties there are in a network, the faster a thing will spread," Dan Centola of the Massachusetts Institute of Technology, whose study appears in the journal Science, said in a statement.
"It's startling to see that this is not always the case."
Knowing how best to influence health behavior is important to health reform as the United States turns its focus to preventing disease, rather than treating it.
Researchers have already shown that networks of friends can have a powerful impact on health behavior, influencing smoking, obesity and even happiness.
But it is not clear which type of network is best.
Social petri dish
Centola set up two different types of social networks within an online community of about 1,500 people.
"I had to create a little social petri dish," Centola said in a telephone interview.
One group consisted of individuals with far-flung ties, and the other involved clusters of people who interacted with each other.
"When people signed up, I would assign them 'health buddies' in the space of this online social networking site," Centola said. To form friendship groups, Centola introduced people to six other people who had similar interests.
"That is the social world that you had," he said.
The goal was to get people to register for a health forum in which they rated different health services.
The team then seeded the groups with people to encourage them to sign up, and they watched to see how quickly people would register.
People in the small friend groups registered four times as fast as those with less connected networks.
"It spread through the population so quickly. It saturates very, very fast," Centola said.
Social scientists had thought that it would be redundant to give a health message to a person more than once. But Centola said when it comes to health habits, people are quicker to change when they hear the message from more than one source.
He said the findings are useful when policymakers need to develop strategies to promote vaccinations or health screenings, but it could be equally effective in combating obesity.
"The more difficult the behavior and the more resistant to change, the more vital these densely clustered ties would be," Centola said.