Is there a shy Tory factor in Brazil?

Today Brazilians go back to the polls for their presidential runnoff between incumbent Dilma Rousseff of the Workers Party (PT) and Aécio Neves of the Social Democrats (PSDB). Neves's performance in round one was considerably better than any of the polls, which led me to examine whether there was a trend (one or two Brazilian friends of mine had suggested there was).

In Britain we know all about the Shy Tory Factor, and I’ll have a detailed report out on British polling shortly. In the US, FiveThirtyEight found that polls are usually systematically biased, but the direction tends to flip about, favouring Democrats one time and Republicans another. Brazil and two-round ballot is harder to examine because there doesn’t seem to be a Brazilian Mark Pack with a readymade spreadsheet of every poll since the war. But it appears to have something really curious… A bias in round one that’s not there in round two.

Here are the last three first rounds, with DKs and refusers left in (there are no WNVs as voting is compulsory for most Brazilian adults). Positive means the polls were too high, negative means too low. The PT vote shares are all predicted to within the margin of error. But the errors on the PSDB shares are huge, and seem remarkably similar to the DK/refusers. I guess they don’t have a spiral of silence adjustment…

But the second round seems to be different. In 2006 there was a switch even bigger than the DKs to the PT’s Lula da Silva (it is possible that there was ‘Shy PT’ factor at work following the Mensalão (kickbacks) scandal, but I don’t have any hard evidence). In 2010 Rousseff’s lead was pretty accurately predicted. So it’s far from clear what will happen this time.

The polls had shown the race as too close to call, with a very slight lead for Rousseff, but since then a swing back in her favour has made her favourite once again. Tonight is looking like a great time to put your feet up with a Guaraná or maybe a Caipirinha, imagine you’re on the beech in Ipanema and enjoy what could be a fascinating political showdown.

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