How Capi works
Three rules: only quality polls enter the main estimate, every uncertainty becomes a simulation and every source is cited.
The best polls
In the US, the average uses the five best-ranked pollsters in the Silver Bulletin accuracy ranking, over the last 45 days, corrected for each one's historical bias. Polls commissioned by parties or campaigns are excluded.
Visible uncertainty
Each forecast runs 10,000 simulations. A national error, shared by every state, is added to a state-specific error that grows when there are fewer polls. That is why we show ranges and chances alongside the median.
Each place against itself
On election night we compare each municipality or county with the previous election, so the order in which votes arrive stops misleading. In Brazil, our projection was within 0.1 point of the result with 59% counted.
Spain, province by province
The national average is spread across the 52 constituencies according to the 2023 result and turned into seats with the D'Hondt method, applying the 3% threshold in each province.
The top US pollsters
| Pollster | Ranking position | Grade |
|---|---|---|
| NYT/Siena | 8 | A |
| Emerson College | 14 | A |
| Fox News (Beacon/Shaw) | 20 | A- |
| Suffolk University | 24 | A- |
| Marist | 29 | A- |
Raters tracked: The Cook Political Report, Decision Desk HQ, The Economist, FiftyPlusOne, Fox News, Inside Elections, MS NOW, NBC News, RealClearPolitics, Sabato's Crystal Ball, Silver Bulletin, Split Ticket.
US model parameters
| Polling window | 45 days |
| National error, Senate (std. dev.) | 3.0 points |
| National error, House | 3.5 points |
| State-level error | 4.0 points with 3+ pollsters; 4.5 with 2; 5.0 with 1; 6.0 with no top pollster |
| House district error | 6.0 points |
| Incumbency advantage | 3 points |
Sources and licenses
TSE (Brazil); Interior Ministry (Spain); Israel's Central Elections Committee; Wikipedia (CC BY-SA) for polling and rating tables; University of Florida Election Lab (CC BY-NC-ND 4.0) for early voting; MEDSL (CC0) for results by vote mode; Silver Bulletin for the pollster ranking.