From Nature:
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.
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