How much polls were off Let's start with the presidential election. Nationally, the polls said Biden would win the popular vote handily — by somewhere around 7.2 percentage points, according to RealClearPolitics' polling average.
That's nearly double the current margin, which stands at 3.8 percentage points, a little more than two weeks after Election Day.
It's a smaller margin than there appeared to be on election night, with votes still waiting to be counted. (New York, for example, had about 84% of its vote total reported as of Wednesday — so this could still shift a bit.)
Meanwhile, polling nearly perfectly captured presidential vote preferences in some battleground states, but it was off by a wide enough margin in others that it threw off election forecasters.
Why the polls were off 1) Who's answering their phones
The polls this year were overwhelmingly off in Biden's favor. That indicates the error was systematic and not random.
"It's safe to say that we don't have enough Republicans in our samples," said Cliff Zukin, a retired professor of political science at Rutgers University who worked in the polling industry for four decades.
To start to explain this, one possibility is partisan non-response.
The Pew Research Center reported in 2019 that the response rate to its phone polls had dropped to 6%, from 36% in 1997. Cellphones and caller ID have a lot to do with this, as many people don't answer calls from numbers they don't recognize.
Certain types of people are also more likely to answer their phones than others. Combine that with shifting partisan alignments among particular demographics, and it can throw polls off.
"You almost always have too many college graduates who took the survey because they're just more amenable to doing it," said Courtney Kennedy, director of survey research at the Pew Research Center. "And in this political era, that's correlated with support for Democrats."
It's also possible that Trump supporters are uniquely averse to answering polls, said Sean Trende, senior elections analyst for RealClearPolitics.
"The No. 1 prediction of being a Trump supporter was agreeing with the statement, 'People like me don't have much say in this country,' " Trende said. "And those are the exact people that when you hear a phone call and the person says, 'Hi, I'm from The New York Times. Would you take a call?' just go click."
On top of that, it's possible that Democrats were especially likely to answer polls this year, as they both were enthusiastic about defeating Trump and isolated themselves at home, David Shor recently told Vox's Dylan Matthews.
"So the basic story is that, particularly after COVID-19, they were donating at higher rates, etc., and this translated to them also taking surveys, because they were locked at home and didn't have anything else to do."
1.5) Weighting
Closely related to that problem of non-response is whether pollsters can adjust for the fact that they had few non-college-graduate respondents — a process called weighting.
In 2016, the American Association for Public Opinion Research found that a failure to weight for education led to an underestimation of Trump support. This year, more pollsters weighted based on education, Kennedy explained, and pollsters were also making sure they had enough Republican respondents.
"And yet we had the results that we did," Kennedy said. "So what does that mean? That means that the Republicans taking the polls may not have been good proxies for all of the Republicans."
One final complicating factor: ultrahigh turnout this year. Pollsters try to figure out what the electorate will look like. But it may have been that predicting that was even harder this year with an electorate that was so much bigger than in recent years.