When US presidential candidate Mitt Romney said last year that he was not even going to try to reach 47% of the US electorate, and that he would focus on the 5–10% thought to be floating voters, he was articulating a commonly held opinion: that most voters are locked in to their ideological party loyalty.

But Lars Hall, a cognitive scientist at Lund University in Sweden, knew better. “His calculation, only zeroing in on 10% of voters, is a risky proposition,” he says. When Hall and his colleagues tested the rigidity of people’s political attitudes and voting intentions during Sweden’s 2010 general election, they discovered that loyalty was malleable: nearly half of all voters were open to changing their minds. The team's work is published today in PLoS ONE1.

Hall’s group polled 162 voters on the streets of Malmö and Lund during the final weeks of the election campaign, asking them which of two opposing political coalitions — conservative or social democrat/green — they intended to vote for, and how strongly they felt about their decision. The researchers also asked voters to rate where they stood on 12 political wedge issues, including tax rates and nuclear power.

The person conducting the experiment secretly filled in an identical survey with the reverse of the voter's answers, and used sleight-of-hand to exchange the answer sheets, placing the voter in the opposite political camp (see video above). The researcher invited the voter to give reasons for their manipulated opinions, then summarized their score to give a probable political affiliation and asked again who they intended to vote for.

No more than 22% of the manipulated answers were detected, and 92% of the study participants accepted the manipulated summary score as their own. This did not surprise Hall, who has previously demonstrated similar reversal effects, known as choice blindness, in people’s aesthetic preferences2 and moral attitudes3.

What is interesting about the latest study is that, on the basis of the manipulated score, 10% of the subjects switched their voting intentions, from right to left wing or vice versa. Another 19% changed from firm support of their preferred coalition to undecided. A further 18% had been undecided before the survey, indicating that as many as 47% of the electorate were open to changing their minds, in sharp contrast to the 10% of voters identified as undecided in Swedish polls at the time.

“It’s a dramatic demonstration of the potential flexibility that is there,” says Hall. “Unfortunately I don’t know how to tap into that flexibility without the magic trick. If I did I wouldn’t be talking to you. I’d be selling my secret to Hillary Clinton or [Republican New Jersey governor] Chris Christie. Or both.” (Clinton and Christie are seen by many as the front-runners for the 2016 US presidential election.)