"The search engine manipulation effect (SEME) and its possible impact on the outcomes of elections", Robert Epstein

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Our results were strong and consistent, but our experiments all involved a foreign election – that 2010 election in Australia. Could voting preferences be shifted with real voters in the middle of a real campaign? We were skeptical. In real elections, people are bombarded with multiple sources of information, and they also know a lot about the candidates. It seemed unlikely that a single experience on a search engine would have much impact on their voting preferences.

To find out, in early 2014, we went to India just before voting began in the largest democratic election in the world – the Lok Sabha election for prime minister. The three main candidates were Rahul Gandhi, Arvind Kejriwal, and Narendra Modi. Making use of online subject pools and both online and print advertisements, we recruited 2,150 people from 27 of India’s 35 states and territories to participate in our experiment. To take part, they had to be registered voters who had not yet voted and who were still undecided about how they would vote.

Participants were randomly assigned to three search-engine groups, favouring, respectively, Gandhi, Kejriwal or Modi. As one might expect, familiarity levels with the candidates was high – between 7.7 and 8.5 on a scale of 10. We predicted that our manipulation would produce a very small effect, if any, but that’s not what we found. On average, we were able to shift the proportion of people favouring any given candidate by more than 20 per cent overall and more than 60 per cent in some demographic groups. Even more disturbing, 99.5 per cent of our participants showed no awareness that they were viewing biased search rankings – in other words, that they were being manipulated.