538: We've Updated Our Pollster Ratings Ahead Of The 2020 General Election
The competitive phase of the 2020 presidential primaries is over — which means we’ve updated FiveThirtyEight’s pollster ratings. These ratings cover this year’s presidential primaries, the 2019 gubernatorial elections and the occasional straggler poll we only just discovered from a past election. They include polls conducted in the final 21 days1 before every presidential, U.S. Senate, U.S. House and gubernatorial general election (including special elections), as well as every presidential primary,2 since 1998. We encourage you to check out the new ratings, especially when a new poll comes out and you want to gauge its reliability.
So far, it hasn’t been a great year for pollsters. The 2020 presidential primary polls had a weighted average3 error — i.e., the absolute difference between a poll’s margin (between the top two candidates) and the actual vote share margin4 — of 10.2 percentage points.5 That’s roughly tied with the 2016 presidential primaries for the biggest error in primary polling this century.
But we don’t blame pollsters too much for this: They have some good excuses because the 2020 Democratic primary race changed so quickly. In the span of a week (from roughly Feb. 25 to Super Tuesday), former Vice President Joe Biden dramatically reversed his electoral fortunes, and surveys just weren’t able to keep up with how fast the mood of the electorate was changing. We can see that by breaking down the error of 2020 primary polls by election date:
Polls of the contests on Super Tuesday had a weighted average error of 12.8 points, with 60 percent of them conducted mostly before Biden’s big South Carolina win and subsequent endorsements by onetime 2020 presidential contenders former South Bend, Indiana, Mayor Pete Buttigieg and Sen. Amy Klobuchar.
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https://fivethirtyeight.com/features/weve-updated-our-pollster-ratings-ahead-of-the-2020-general-election/