The latest polls just released tonight are suggesting a numerical tie between Dilma Rousseff (PT) and Aecio Neves (PSDB) considering the limit of the margin of error. Actually, these polls fired up a possible game-changing for the opposition over the government as some of the polls did capture any impact stimulated by the televised debate on Friday night.
There is still a lot of uncertainty around; roughly 5% of the electorate were reported to be undecided still. Nonetheless, by the time I run my model today, it turned Aecio ahead of Dilma for a little margin (< 1%). These numbers also account for Wasting votes, so it will typically diverge from the official results.
Although the machinery behind the model I'm running allows for drawing several elections from data, it's too risky to call one side or the other given the pollster's credibility, which was certainly aggravated by the poor performance 3 weeks ago. Meanwhile, I've been trying to learn the pollsters' random walk in the Brazilian campaigns, but given the small range of observations this will take a while to produce robust measures.
The following chart shows the house effects considering those polls released over the runoff campaign. Ideally, a poster would have its effect equally distributed between positive and negative bands. Like a drunkard's walk a pollster could stagger left and right near each party or candidate. Not surprisingly, however, the picture shows two blocks of bias. While the first 4 pollsters typically fielded more positive numbers of the Government, the last 3 did so for the opposition. In addition, the house effects found for Datafolha, Veritá, and Sensus are statistically different than zero.
Taking a less systematic approach on the house effects, adjusting only for the sample size of the polls, regardless the methodology employed (probability with quotas or simply quotas), Dilma appears ahead with an interval of [2.5% to 5.7%] as represented in the following distribution. This happen because polling firms with a house house effects toward the government happen to sample much more people than otherwise, though the methodology they use to sample a large quantity of voters is poorer. This election is so mercurial that wrong decision on the precision parameter can sway the outcome from one side to the other.