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Just how much can activity on Facebook influence the real world? About 340,000 extra people turned out to vote in the 2010 US congressional elections because of a single election-day Facebook message, estimate researchers who ran an experiment involving 61 million users of the social network.

The study, published today in Nature1, is the first to demonstrate that the online world can affect a significant real-world behaviour on a large scale, say the researchers. But the closest Facebook friends exerted the most influence in getting users to the ballot box.

Some people think there is no way that the online world can have an effect on real life; others argue that social media is so influential that the Arab Spring was catalysed by networking sites, says James Fowler, a political scientist at the University of California, San Diego, who led the study in collaboration with Facebook's data-science team.

“Our study shows that the truth is somewhere in between: online networks are powerful ... but it is those real-world ties that we have always had that are making a difference,” he says.

Social pressure

The experiment assigned all US Facebook users who were over 18 and accessed the website on the 2 November 2010 — the day of the elections — to one of three groups.

About 611,000 users (1%) received an 'informational message' at the top of their news feeds, which encouraged them to vote, provided a link to information on local polling places and included a clickable 'I voted' button and a counter of Facebook users who had clicked it. About 60 million users (98%) received a 'social message', which included the same elements but also showed the profile pictures of up to six randomly selected Facebook friends who had clicked the 'I voted' button. The remaining 1% of users were assigned to a control group that received no message.

The researchers then compared the groups' online behaviours, and matched 6.3 million users with publicly available voting records to see which group was actually most likely to vote in real life.

The results showed that those who got the informational message voted at the same rate as those who saw no message at all. But those who saw the social message were 2% more likely to click the 'I voted' button and 0.3% more likely to seek information about a polling place than those who received the informational message, and 0.4% more likely to head to the polls than either other group.

The social message, the researchers estimate, directly increased turnout by about 60,000 votes. But a further 280,000 people were indirectly nudged to the polls by seeing messages in their news feeds, for example, telling them that their friends had clicked the 'I voted' button. “The online social network helps to quadruple the effect of the message,” says Fowler.

Close and personal

Only close friends influenced users to vote in the real world. Facebook users have an average of about 150 friends, but they are likely to have close relationships with only 10. “The closest 10 friends on Facebook mattered; the other 140 didn't matter at all,” says Fowler.

Researchers praised the study for the issue it tackled and its scale. One of the most pressing questions in collective human behaviour is whether social-network platforms can change mass behaviour, says Brian Uzzi, a sociologist at Northwestern University in Evanston, Illinois.

But others add that further research is needed. It is important to pin down why exactly a user is more likely to vote if their close friends do, says Michael Macy, a networks expert at Cornell University in Ithaca, New York.

Overall, the experiment had an effect towards the lower end of what 'get out and vote' campaigns can achieve, says Fowler: door-knocking campaigns can increase voter turnout by about 8%, for example, whereas e-mail campaigns achieve gains of 1% or less, he says. But, Fowler adds, the audience for social networks is large and the study's estimates were conservative, because, for example, many users may have logged onto Facebook too late for the messages to have an effect. Fowler emphasizes that behaviours other than voting won't necessarily be influenced in the same way.

Cameron Marlow, head of Facebook's data-science team and a co-author of the paper, stresses that individuals' identities had been protected in the study. He declined to comment on whether Facebook would deploy any message to help to increase voter turnout at this year's US presidential election.