An almost 10% error rate even by the best on the list for primaries….
So the ratings have not changed very much. The top-rated pollsters — Selzer & Co. and The New York Times/Siena College — will be familiar to longtime readers. For the record, though, eligible polls in the 2024 presidential primaries missed the final margin between the top two candidates by an average of 9.7 percentage points.4That isn’t very accurate, obviously — but it’s consistent with the long-term average error in presidential primary polls since 2000, which is 9.3 percentage points.
Since there aren’t any methodological changes, let’s just go ahead and get to the numbers. (If we’re being honest, I’m not too interested in engaging in public debates about the merits of individual pollsters anyway.) The columns in the pollster ratings table are as follows5:
- An overall grade based on a pollster’s predictive plus-minus rating. Grades for pollsters with sparse data are rounded (e.g. to “A/B” rather than A-) and banned pollsters6 automatically receive a grade of F.
- The predictive/plus minus rating itself, which is how accurate the model expects the pollster to be going forward based on a combination of its historical accuracy and its transparency/disclosure standards — pollsters get a bonus if they’re either a member of the AAPOR Transparency Initiative or share their data with the Roper Center archive. Negative plus-minus scores are good and imply that we expect the pollster to be more accurate than average going forward.
- Mean-reverted bias — that is, a pollster’s historical average statistical bias toward Democratic or Republican candidates, reverted to a mean of zero based on the number of polls in the database. This is calculated only for races in which exactly one Republican and one Democrat are the two leading candidates (so it doesn’t apply for presidential primaries, for instance). A score of “D +1.5”, for example, means that the pollster has historically overrated the performance of Democratic candidates.
- Finally, the number of polls included in the calculation. The database goes back to 1998, though polls from more recent years are weighted more heavily. In general, these ratings cover all polls in the 21 days prior to presidential, Congressional and gubernatorial general elections, and presidential primaries….
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The goal is to launch the forecast at some point during the week of June 24, as the first presidential debate will be held on June 27. There’s a fair amount of work still to do, but I think I’m on track to hit that deadline, with help from the fabulous new Silver Bulletin assistant elections analyst, Eli McKown-Dawson…..