On the morning of 4 October, before Brazil’s polls opened, we forecast that Lula would win 45.12% of valid votes in the first round. He won 45.16%.
To compare with the polls, we use the Ranking dos Políticos polling aggregator, which averages the main Brazilian pollsters in valid votes. On election eve it had Lula at 45.3%, Flávio Bolsonaro at 43.2% and the gap between them at 2.1 points. Across the final three weeks of the campaign, our forecasts were closer to the result than that average on all three forecasts.
Every Mantic forecast linked below is a snapshot frozen before the vote.
Lula: 45.12% forecast, 45.16% result
Our final forecast put Lula at 45.12%, with an 80% range of 42.7% to 47.6%, and a median of 45.17%. He won 45.16%: a miss of 0.04 points on our most likely value and 0.01 points on the median. The polling average missed by 0.14 points.
Flávio: 44.69% forecast, 47.03% result
We forecast 44.69% for Flávio, with an 80% range of 41.9% to 47.9%. He won 47.03%. The polling average had him at 43.2%: it missed by 3.8 points, we missed by 2.3.
Our forecast started from the polling average and added two adjustments: late consolidation of minor candidates’ voters, and a partial correction for the polls’ underestimate of the right in 2018 and 2022.
The gap: Lula +1.05 forecast, Flávio +1.87 result
With other candidates in the race, it was worth independently forecasting the gap between the two front-runners. We forecast Lula ahead by 1.05 points, with an 80% range from Flávio +3.5 to Lula +5.2. Flávio won by 1.87 points. The polling average had Lula ahead by 2.1: it missed the gap by 4.0 points, we missed by 2.9.
Over the last two weeks of the campaign, our forecast of Lula’s lead stayed between 1.4 and 2.4 points, while the polling average ranged from 2.5 to 3.9.
Not just on election morning
We compared each of our updates from 14 September (16 September for the gap) to 2 October with the polling average on the day before. Using our medians, our average miss was 1.0 points on Lula against 1.6 for the polls, 5.2 against 6.5 on Flávio, and 4.0 against 5.0 on the gap.
On Flávio and on the gap, we were closer than the polling average at every update. On Lula, at six of eight. Our Flávio forecast rose from 38.7% on 14 September to 42.7% on 2 October, above the polling average throughout.
What’s next: the 25 October runoff
We now give Flávio an 80.8% chance of winning the presidency, against 18.9% for Lula. On 2 October, before the first round, we had him at 57.8%.
We featured Lula’s first-round vote share before the vote in our latest edition of Friday Forecast, the Election Bonanza, with forecasts on the US midterms, Brazil, France, Israel and Nigeria. For how our forecasts compare with prediction markets over a longer period, see our backtest against Polymarket.
