Back to the forecast · How the forecast works
Every poll, and how much it counts
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- 1. CheckedOnly polls naming the candidates actually on the ballot. The same poll reported by two sources is kept once.
- 2. CorrectedFor the pollster's measured lean (or its campaign sponsor's), and for the state's persistent polling miss in the last two elections.
- 3. WeightedBy precision: fewer undecideds, no strong third candidate, an experienced pollster and a recent field date all count for more. Campaign polls count for 0.58.
- 4. BlendedWith the race's fundamentals. A poll far from the others is partly discounted as a likely outlier, and every race keeps a shared polling-miss floor.
The national generic ballot and presidential approval are fitted as one smooth trend through every poll, with each pollster's lean and the gap between likely voters, registered voters and all adults estimated at the same time. Weight is what the poll brings into the fit: the square root of its sample size (100–3,000), halved for partisan or internal polls, reduced when a tracking poll's field overlaps its previous release, and split between versions of the same survey. Influence on today is how much the poll moves today's trend value: recent, large polls carry the estimate, and polls from months ago contribute almost nothing even at full weight. Polls from the last 150 days.