Facebook field experiment shows strong ties affect voter turnout

The most recent Nature features an article by a team of political scientists and network scholars who did an experiment using Facebook to show that strong ties influenced voting behavior in the last election. You may say, so what? We’ve known for a long time that social influence operates through strong ties in interpersonal networks. That’s not a new insight.  But I think the study is innovative for a couple of reasons. The first is that the impact of of using direct messaging through Facebook was substantively significant  – that is, just messaging people reminders to go out and vote increased the likelihood that the person would vote – but that the larger effect was transmitted indirectly via social contagion. Consider the setup of the experiment.

To test the hypothesis that political behaviour can spread through an online social network, we conducted a randomized controlled trial with all users of at least 18 years of age in the United States who accessed the Facebook website on 2 November 2010, the day of the US congressional elections. Users were randomly assigned to a ‘social message’ group, an ‘informational message’ group or a control group. The social message group (n = 60,055,176) was shown a statement at the top of their ‘News Feed’. This message encouraged the user to vote, provided a link to find local polling places, showed a clickable button reading ‘I Voted’, showed a counter indicating how many other Facebook users had previously reported voting, and displayed up to six small randomly selected ‘profile pictures’ of the user’s Facebook friends who had already clicked the I Voted button (Fig. 1). The informational message group (n = 611,044) was shown the message, poll information, counter and button, but they were not shown any faces of friends. The control group (n = 613,096) did not receive any message at the top of their News Feed.

People in the social message group were 2% more likely to click on the I Voted button than people who merely received the informational message. Both groups, of course, were more likely to vote than the control group.  Moreover, the effect was accentuated by your close friends receiving the social message. For each close friend who received the social message, a person was .22% more likely to vote.  In short, the study shows that a simple message that conveys friends’ voting behavior significantly increases your own likelihood of voting.  The increase in probability may seem small, but when the effect is accentuated by the number of friends who report voting, it can lead to noticeable differences in aggregate voter outcomes.  The results “suggest that the Facebook social message increased turnout directly by about 60,000 voters and indirectly through social contagion by another 280,000 voters, for a total of 340,000 additional votes. That represents about 0.14% of the voting age population of about 236 million in 2010.”

And this brings up the second reason this study is innovative. The study conducted this experiment using 61 million Facebook users as test subjects! That’s an enormous project. I’ve never heard of a field experiment carried on that scale. The analysts can precisely identify what impact their experiment had on the election voter turnout because they had such a large pool of test subjects. It’s really amazing that social science can engage in an experiment of this size.

Here’s the abstract:

Human behaviour is thought to spread through face-to-face social networks, but it is difficult to identify social influence effects in  observational studies, and it is unknown whether online social networks operate in the same way. Here we report results from a randomized controlled trial of political mobilization messages delivered to 61 million Facebook users during the 2010 US congressional elections. The results show that the messages directly influenced political self-expression, information seeking and real-world voting  behaviour of millions of people. Furthermore, the messages not only influenced the users who received them but also the users’ friends, and friends of friends. The effect of social transmission on real-world voting was greater than the direct effect of the messages  themselves, and nearly all the transmission occurred between ‘close friends’ who were more likely to have a face-to-face relationship.  These results suggest that strong ties are instrumental for spreading both online and real–world behaviour in human social networks.