Over 44 days, the apps of nearly 8000 users sent over 40,000 notifications to 1.3 million friends, and about 1000 of those friends adopted the app. Aral and Walker then built a model of the app's "contagion" through this massive social network. If the influentials hypothesis is true, most of the spread should be catalyzed by a small number of key people.
Reality seems to fall somewhere between influence and susceptibility. Both are important, but contagion depended on the personal traits of the people, the team reports online Thursday in Science. For example, people older than 30 were more influential than those who are younger than 30, and people of the same age had the most influence on each other. Women tended to influence men more than they influenced each other. But most surprisingly, influence and susceptibility almost never occurred in the same person. At least in the Facebook network, there are only trendsetters and followers.
The study is on "a phenomenally large scale," says Brian Uzzi, a social scientist at Northwestern University in Evanston, Ill. The division between influence and susceptibility could have a large influence on online marketing, he says, allowing companies to predict not only whether you will be interested in a particular product, but also whether you're the kind of person who can help it go viral. However, says Uzzi, "to know if virtual world social influence substitutes, complements, or is independent of the real world, we need another experiment that looks at the diffusion of the same product on Facebook and [in] the real world."
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This is adapted from ScienceNOW, the online daily news service of the journal Science. http://news.sciencemag.org