Pollsters face another reckoning this year, but the reasons could differ from 2016

Once again, public opinion polls missed the mark on the U.S. presidential election.

The polls largely indicated a Democratic sweep with former Vice President Joe Biden up an average of 7.4 percentage points ahead of President Donald Trump in national polls, according to NBC News’ polling average. Polls indicated Biden could win Wisconsin at 6.7 percentage points ahead of Trump, according to a RealClearPolitics average, although preliminary election results show the candidates are less than a percentage point apart.

Polls on average also predicted Biden would win Florida by nearly a full percentage point, according to RCP. Instead, Trump won the state by more than three percentage points, according to NBC News projections.

But the reasons for the disparity could vary from those in 2016, polling experts told CNBC. Pollsters faced a public reckoning after failing to predict former Secretary of State Hillary Clinton’s defeat by Trump. Since then, the industry made changes seeking to diminish the error in their methods.

“When polls go bad, when polls mislead, they do so in different ways,” said W. Joseph Campbell, a professor of communication at American University and author of “Lost in a Gallup: Polling Failure in U.S. Presidential Elections.”

“No two polling failures are quite alike and I think that held in this year,” Campbell said. “2020 is not the same kind of polling surprise as it was in 2016.”

Polling groups took stock of the failures in 2016 and tried to adjust, as they always do. A post-mortem by the American Association for Public Opinion Research (AAPOR) found that polls ahead of the 2016 election mainly underestimated support for Trump in places like Michigan, Pennsylvania and Wisconsin, which Trump flipped from blue to red that year.

AAPOR found that failing to weight results based on education level was a likely source of error in the polls, among others. Education level was later found to be highly correlated with voters’ preferences in key states, according to the report, though pollsters still disagree on the importance of this factor in accounting for the error.

Overall, AAPOR found that national polls in 2016 were not all that far off, showing a 3 percentage point lead for Clinton in the popular vote, which she ultimately won by 2 percentage points. Even many state-level polls “showed a competitive, uncertain contest,” AAPOR found, and said that on average, they “indicated that Trump was one state away from winning the election.”

This year, many polls appear to have been directionally correct based on preliminary vote counts which exclude many outstanding and mailed ballots. Charles Franklin, who directs the Marquette Law School Poll, calculated that more than 90% of polls got the winner right in states that had been called as of early Friday afternoon.

But on average, he said of the races called so far, the polls overestimated Biden’s lead by 5.8 percentage points. He said he he did not have data on six states not yet called as well as Mississippi or Massachusetts.

Franklin said the error this year seemed to be more broad.

“In 2020, rather than having that error focused in just a handful of states, this year really it looks like it was quite widespread,” he said. “I can’t find any state where the polling error was in Trump’s favor.”

While it’s too early to fully assess what went wrong this year, especially with many still votes still outstanding, pollsters have some early questions. Those range from how record turnout could impact the numbers to how Trump himself might have.

“There’s no single answer to why the polls surprised us in 2020,” Campbell said.

Article source: https://www.cnbc.com/2020/11/07/election-pollsters-2020-reckoning.html