Manipulation effect tested on undecided Indian voters.
Search engines can influence voters without them noticing, new research has found.
Psychologist Robert Epstein, whose most recent findings were released on Monday, coined it the Search Engine Manipulation Effect.
Epstein, who is a critic of Google, extended his research on the effect during India's national elections.
The latest experiment, conducted with a group of more than 1,800 undecided Indian voters, was able to shift votes by a 12.5% average by altering candidate rankings in Google search results. Only one in every 100 participants noticed the intentional manipulation.
Participants, who were found by advertising for undecided voters for India's election, were made to sign on to a Web portal, and were then presented with a Kaboodle search engine and asked to find out information on candidates. The portal was, however, rigged, and each of the participants was assigned to a group favouring one of the candidates.
Epstein, who is a senior research psychologist at the American Institute for Behavioral Research and Technology, said: "It confirms that in a real election, you can really shift voter preferences really dramatically."
However, sceptics of Epstein said that voters are influence by many more sources than search engine results, so the effect can not be the ultimate factor in deciding a vote. Furthermore, search engine operators would face major public and political backlash if it was found that results were manipulated.
Google officials have said in a statement responding to Epstein's research: "Providing relevant answers has been the cornerstone of Google's approach to search from the very beginning. It would undermine people's trust in our results and company if we were to change course."
But Epstein said: "Even if you're not doing it deliberately, you are driving votes. They are running a system that is determining the outcome of elections."