Facebook study reveals what makes someone a leader

Every group of friends has its leaders and its followers, those who are able to influence their peers and those who can't resist. Now a study of over one million Facebook users reveals just who wields the most peer power, with men showing greater influence than women, while younger people are less influential than their older counterparts.

Knowing what makes someone influential could of course help advertisers spread their products through social media, but it can also be used more altruistically, such as promoting HIV testing in Africa. "Finding influential people is all the rage today," says Sinan Aral, who studies the spread of information at New York University. But he says that many companies who claim to measure influence online are not approaching it in a scientific way.

Aral and his colleague Dylan Walker, also at NYU, studied influence by watching how use of a film-rating app spread through Facebook users. Starting with a seed group of 7730 users, the researchers designed the app to randomly send messages to the app users' friends, encouraging them to also install the app. Just under 42,000 messages were sent out to a random selection of the initial groups' 1.3 million friends, resulting in nearly 1000 new app users.

This random selection of who gets the message allowed the researchers to avoid common pitfalls in measuring influence, such as homophily bias ? the principle that we tend to make friends with people like ourselves. "If two friends adopt a product one after the other, current methods have a hard time distinguishing whether it is because of peer influence, or rather that the friends simply have similar preferences," explains Aral.

Who are the power brokers?

Analysing the results in combination with users' Facebook profile data revealed a number of insights into which people are the most influential. Men are 49 per cent more influential than women, but women are 12 per cent less susceptible to influence than men, and they exert 46 per cent more influence over men than over other women. Influence also increases with age, with people over 31 being 51 per cent better at convincing their friends than those under 18.

Relationship status also plays a role. Single individuals are 113 per cent more influential than those in a relationship and 128 per cent more than those who define their relationship status as "it's complicated". On the flip side, susceptibility rises with increasing relationship commitment ? up until you get married.

Aral says that statistics cannot explain why these effects occur, but one possible reason is that those in more serious relationships have greater obligation to respond to requests from their partner's family, with social pressure easing once you get married. "It may be more difficult to reject a request from one's future father-in-law just before the wedding," he says. "After the marriage, all bets are off."

"This is probably the first experimental contribution to the long-standing question of influence and susceptibility," says Manuel Cebrian who studies social networks at the University of California, San Diego. He adds that Aral and Walker's findings are much more significant than previous attempts to measure influence because of their statistical validity.

Journal reference: Science, DOI: 10.1126/science.1215842

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