Are Brazil’s pollsters right about the presidential election?

Just after 8am on September 27th, five days before the first round of a presidential election, a worker from Brazil’s most prominent polling firm, Datafolha, stops pedestrians at a five-way intersection in São Paulo to ask whom they plan to vote for. He selects his subjects—an old man in a baseball cap, a young woman with a nose piercing—according to age and sex quotas that reflect the electorate. He asks them to point to their candidate’s name on a chart (circular, to lessen bias), and records their answers on a tablet.

Over the next few days 440 Datafolha workers in 332 municipalities planned to speak to some 6,800 voters. Within hours of the final interviews, the results would be announced on a nightly news programme watched by a third of Brazilian households.