Epstein & Robertson (2015)

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PNAS(peer-reviewed)·pnas.org/doi/10.1073/pnas.1419828112

Authors

Epstein, Robert·Robertson, Ronald E.

Credibility Rating

5/5

Gold(5)

Gold standard. Rigorous peer review, high editorial standards, and strong institutional reputation.

Rating inherited from publication venue: PNAS

Foundational empirical study on how algorithmic ranking systems can covertly manipulate democratic outcomes; directly relevant to concerns about AI systems influencing human beliefs and decisions at scale without user awareness.

Metadata

Importance: 72/100journal articleprimary source

Summary

Epstein & Robertson (2015) demonstrate through five randomized controlled experiments with 4,556 undecided voters that biased search engine rankings can shift voting preferences by 20% or more without users' awareness. The study introduces the 'Search Engine Manipulation Effect' (SEME), showing that a dominant search engine company could covertly influence election outcomes at scale, particularly in countries with limited search engine competition.

Key Points

•Biased search rankings shifted undecided voter preferences by 20%+ in controlled experiments across the US and India, with larger effects in some demographic groups.
•Crucially, manipulation could be masked so users showed no awareness of the influence, making SEME a covert and deniable form of persuasion.
•The fifth experiment was conducted with real eligible voters during India's 2014 Lok Sabha elections, demonstrating real-world applicability.
•Given that many elections are decided by small margins, a single dominant search engine theoretically has the power to sway numerous elections undetected.
•SEME may generalize beyond elections to influence a wide range of attitudes and beliefs, raising broader concerns about algorithmic control over public opinion.

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Contents

## Significance

We present evidence from five experiments in two countries suggesting the power and robustness of the search engine manipulation effect (SEME). Specifically, we show that ( _i_) biased search rankings can shift the voting preferences of undecided voters by 20% or more, ( _ii_) the shift can be much higher in some demographic groups, and ( _iii_) such rankings can be masked so that people show no awareness of the manipulation. Knowing the proportion of undecided voters in a population who have Internet access, along with the proportion of those voters who can be influenced using SEME, allows one to calculate the win margin below which SEME might be able to determine an election outcome.

## Abstract

Internet search rankings have a significant impact on consumer choices, mainly because users trust and choose higher-ranked results more than lower-ranked results. Given the apparent power of search rankings, we asked whether they could be manipulated to alter the preferences of undecided voters in democratic elections. Here we report the results of five relevant double-blind, randomized controlled experiments, using a total of 4,556 undecided voters representing diverse demographic characteristics of the voting populations of the United States and India. The fifth experiment is especially notable in that it was conducted with eligible voters throughout India in the midst of India’s 2014 Lok Sabha elections just before the final votes were cast. The results of these experiments demonstrate that ( _i_) biased search rankings can shift the voting preferences of undecided voters by 20% or more, ( _ii_) the shift can be much higher in some demographic groups, and ( _iii_) search ranking bias can be masked so that people show no awareness of the manipulation. We call this type of influence, which might be applicable to a variety of attitudes and beliefs, the search engine manipulation effect. Given that many elections are won by small margins, our results suggest that a search engine company has the power to influence the results of a substantial number of elections with impunity. The impact of such manipulations would be especially large in countries dominated by a single search engine company.

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Recent research has demonstrated that the rankings of search results provided by search engine companies have a dramatic impact on consumer attitudes, preferences, and behavior ( [1](https://www.pnas.org/doi/10.1073/pnas.1419828112#core-collateral-r1) – [12](https://www.pnas.org/doi/10.1073/pnas.1419828112#core-collateral-r12)); this is presumably why North American companies now spend more than 20 billion US dollars annually on efforts to place results at the top of rankings ( [13](https://www.pnas.org/doi/10.1073/pnas.1419828112#core-collateral-r13), [14](http

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