from The Washington Post,
7/18/21:
... the American Association for Public Opinion Research (AAPOR) task force found that the surveys overstated the margin between President Biden and former president Donald Trump by 3.9 points in the national popular vote and 4.3 percentage points in state polls.
Polls understated the support for Trump in nearly every state and by an average of 3.3 percentage points overall. Polls in Senate and gubernatorial races suffered from the same problem.
“There was a systematic error that was found in terms of the overstatement for Democratic support across the board,” said Josh Clinton, a Vanderbilt University political science professor who chaired the 19-member task force.
The polls did a better job of estimating the average support for Biden, with a few exceptions. In general, support for Biden in the polls was 1 percentage point higher than his actual vote.
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