Edited by Jacob N. Shapiro, Princeton University, Princeton, NJ, and accepted by the Editorial Board July 8, 2015 (received for review October 16, 2014)
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.
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.
Author contributions: R.E. and R.E.R. designed research, performed research, contributed new reagents/analytic tools, analyzed data, and wrote the paper.
The authors declare no conflict of interest.
*Although all participants claimed to be eligible voters in the prescreening, we later discovered that 6.9% of subjects marked “I don't know” and 5.2% of subjects marked “No” in response to a question asking “If you are not currently registered, are you eligible to register for elections?”
†As in study 1, although all participants claimed to be eligible voters in the prescreening, we later discovered that 4.7% of subjects marked “I don't know” and 2.6% of subjects marked “No” in response to a question asking “If you are not currently registered, are you eligible to register for elections?”
‡Degrees of freedom adjusted for significant inequality of variances (Welch’s t test).
§English is one of India’s two official languages, the other being Hindi.
¶Some of the data applied in the analysis in this publication are based on material from the “European Election Database.” The data are collected from original sources and prepared and made available by the Norwegian Social Science Data Services (NSD). NSD is not responsible for the analyses/interpretation of the data presented here.
||A mathematical model we developed—highly conjectural, we admit, and at this point unverifiable—shows the possible dynamics of such synergy (Fig. S1).
This article is a PNAS Direct Submission. J.N.S. is a guest editor invited by the Editorial Board.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1419828112/-/DCSupplemental.
Freely available online through the PNAS open access option.
