The influence occurred even though the research participants were not Facebook friends or even acquaintances of the commenters. In fact, the commenters - like the candidate himself - did not even exist, researchers said.
University of Delaware researchers created a Facebook page for a fictitious candidate using general and nonpartisan "information" about him.
Delawareans selected as a test group were sent an online survey, asking them to look at the page and then rate their impressions of the candidate. Some of the recipients saw a page with two fictitious supportive comments, while others saw two challenging comments.
"We wanted to test this interactivity between the candidate and citizens," he said.
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Researchers found that those who saw positive comments or "likes" had a more favourable perception of the candidate and were more likely to support him, while those who saw the negative comments had more unfavourable perceptions.
Whether the candidate responded to the comments had no effect on how he was perceived.
"It's the idea that what other people say about you is genuine, perhaps unlike what you say about yourself. So comments from some random person on the Internet do shape citizens' perceptions," he said.
Calling the study a first step in researching the effect of social media interactivity in political campaigns, Brewer said that it may have been easier to influence viewers looking at the "blank slate" of a fictitious candidate rather than at a real candidate with whom they may already be familiar.
"Candidates have long used carefully orchestrated social cues, from endorsements to photo opportunities to stage-managed public events, in their efforts to persuade voters that they are riding a wave of popular support," the researchers said in the study published in the Journal of Experimental Political Science.
"The increasing use of [social networking sites] by voters provides candidates and other actors with new tools for projecting images of popularity or unpopularity in ways that may carry electoral consequences," they said.