How to Read a Polling Average
A polling average is the most useful single number we publish — and the most commonly misread. Here is what it tells you, what it doesn't, and how to use it well.
What an average is — and isn't
A polling average combines recent surveys so that no single poll dominates. It answers one question: across the polls taken so far, where does each candidate's support stand? That makes it a snapshot, not a prediction. A candidate at 47% in the average is polling at 47% — that is not a “47% chance of winning,” and it is not a promise of 47% on election day. Opinions move, some voters decide late, and polls themselves carry error.
Why the average moves
The average changes for two very different reasons, and it pays to tell them apart. The first is real movement: voters changing their minds, usually in response to news or campaign events. The second is composition: a new poll enters the window, an old one fades out, and the mix of pollsters shifts. If a firm that tends to show one party doing well publishes today and a different firm published last week, the average can tick up or down with no actual change in opinion.
The practical habit: ignore day-to-day wiggles and read the trend over weeks. A sustained move confirmed by several pollsters is signal; a one-day bump from a single poll usually isn't.
How weighting works, in plain English
Not every poll deserves an equal vote, so our average weights each one on four ideas:
- Freshness. Newer polls count more. In our average, a poll's weight halves every two weeks, so old surveys fade out gradually rather than being cut off.
- Track record. Pollsters with a history of accuracy and transparent methods get more weight than those without.
- Sample size. Bigger samples help, but with diminishing returns — quadrupling the sample doesn't quadruple the reliability, and no poll is allowed to dominate on size alone.
- Sponsorship. Polls sponsored by campaigns or partisan groups still contain information, so we discount them rather than discard them.
Every multiplier behind those four ideas is published, with the source code linked, on our methodology page. We'd rather you check the math than take our word for it.
Margin of error, intuitively
A poll asks a sample of people, not everyone, so every number it reports is an estimate with a range around it. The “margin of error” a pollster reports describes that sampling luck: interview a different random sample and you'd get a slightly different number. Two things follow. First, a candidate “at 47%” is really somewhere in a band around 47%. Second, the gap between two candidates is noisier than either number alone, because both estimates wobble — a small lead in one poll is weak evidence by itself.
Averaging many polls shrinks that random wobble. What it cannot fix is shared error: if most pollsters underestimate the same group of voters, their polls miss in the same direction, and the average misses with them. Polling history includes cycles where that happened. That is why we describe a close average as a close race — not as a leader and a trailer.
Go deeper
The exact formula — every weight, grade table, and constant — is on the methodology page. For why two well-run polls can still show different numbers, see Why Polls Disagree.