Blind data

WHIZZY statistical models were ten-a-penny during the presidential election in the United States in 2012, when Nate Silver and fellow “forecaster-pundits” produced uncannily accurate predictions of a solid win for Barack Obama. In Brazil, where voters will cast first-round ballots on October 5th, they remain scarce. Election-watchers prefer instead to divine trends, poll by poll. The latest show Dilma Rousseff, the left-wing incumbent, opening up a lead of six to eight percentage points over Marina Silva, her nearest challenger, in a likely second-round run-off later this month.

Models come in three broad types. The first, made famous by Mr Silver, takes polls released each week, then aggregates and weights them to come up with a prediction. Another looks at how “fundamentals”—which can mean anything from unemployment to government-approval ratings—have shaped past elections. A hybrid approach mixes the two, increasing the weight of the polling data as election day draws nearer.