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A few months ago, I sketched preliminary explanations of last November’s election; those conclusions still hold up well. This post addresses how well–or, poorly–the election polling did, why, and with what implications for using polls as a voice of popular opinion.Truman-Dewey

Putting the major polls together, their miss in last year’s presidential election was, on average, 4 percentage points, mainly because they underestimated the Trump vote; they also underestimated the Republican down-ballot votes by about the same margin. (Fivethirtyeight.com’s final averages of polls gave Biden an 8.4-point lead; he ended up winning by 4.4 points.) As presidential elections forecasting in recent decades go, this error was roughly average.

However, the 2020 polling stirred considerable and appropriate consternation; Politico declared the morning after that “the polling industry is a wreck and should be blown up.” The reasons for consternation include these:

* Although the polls got the electoral college winner right this time, the 2020 error was actually larger than the 2016 error, which was only 1.8 percentage points (Clinton was predicted to win the popular vote by 3.9 points, but won it by 2.1 points).

* This deterioration in accuracy occurred despite major efforts by polling organizations to fix the apparent 2016 problems and notable improvement in the 2018 off-year elections. The average 2018 error in forecasting party shares of the congressional vote was exactly zero. FiveThirtyEight.com declared that the “Polls are Alright.”

* In particular states (e.g., Wisconsin, Florida) the 2020 presidential polling error was much larger than the national 4 points.

* Many projections for down-ballot races, such as the Senate race in Maine, performed a lot worse than the presidential ones.

* The polls’ errors leaned in the same direction as in 2016, underestimating the Republican vote yet again.

Post mortems on the election now have some analysts and some political action groups (e.g., Swing Left) looking to rely less on polling going forward and more on “fundamentals” such as how a district voted in prior elections.

What happened?

(more…)

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