Why polls keep getting it wrong on Brazil's right

Once again, Brazilian pollsters missed the mark in a first-round election on Sunday, joining many around the world who have struggled to gauge support for the right from voters who can be cagey about their choices.

"I am very pleased because many polling institutes had us trailing," right-wing Senator Flávio Bolsonaro said after edging past President Luiz Inácio Lula da Silva in Sunday's election.

He is now a firm favourite as the race goes to a run-off vote on October 25.

The son of far-right former president Jair Bolsonaro, the opposition candidate secured nearly 47 percent of the vote, compared to Lula's 45 percent.

The Datafolha pollster had Lula three percentage points ahead of his rival in the first round, while Quaest showed a one-point lead for Lula.

Survey firms have been blindsided in other countries too.

In the United States, some polls wrongly predicted a victory for Democrat Kamala Harris over Donald Trump in the 2024 elections.

In Latin America, polls also failed to anticipate the strong showing of libertarian firebrand Javier Milei in Argentina or conservative Rodrigo Paz in Bolivia.

Right-wing and far-right forces in Europe have also bucked predictions.

In many cases, these parties have positioned themselves as anti-establishment options and capitalize on social discontent. 

"There is the phenomenon of the 'shy vote' phenomenon, where voters don't choose a candidate on their merits, but because they dislike the other options," Marco Carvalho Teixeira, a political scientist at the Getúlio Vargas Foundation, told AFP.

Such voters will not disclose their choice to pollsters.

Brazil's first-round election also featured "high volatility" among undecided voters right up to the end of the campaign, making predictions difficult, says Carvalho Teixeira. 

James Bosworth, a consultant and author of the Latin American Risk Report, a political risk newsletter, said pollsters overestimated the support of third-party candidates who garnered only eight percent of the vote on Sunday.

He said some voters who had expressed support for one of the smaller candidates "voted strategically" and opted for one of the leading candidates in a bid to make their vote count – which Bolsonaro had pushed hard for on the campaign trail.

Nevertheless, the polling error was smaller this year than in the first round of elections in 2022 when polls gave Lula a 10-point advantage over Jair Bolsonaro. He came first by only five.

"In the last four elections, the Brazilian right performed three to four percent better than the polls predicted," Bolsonaro's campaign manager, Senator Rogerio Marinho, told AFP ahead of the vote.