Washington Post, November 2020
Each campaign season, pollsters conduct hundreds of pre-election surveys, feeding the apparently endless public and news media appetite for agonizing over the poll results. When the polls don’t accurately forecast the final election results, many are disillusioned or even angry. That was especially true in 2016, when most national polls projected that Hillary Clinton would win the presidency.
So how did pollsters do in 2020?
After 2016, pollsters worked to fix problems
After the 2016 election, we worked with political scientist Aaron Weinschenk to release analyses, revealing 2016’s final, national pre-election polls were actually more accurate than they had been in 2012. They pretty closely forecast the popular vote, even if Donald Trump snagged victory in the electoral college. We found a slight pro-Democratic bias that was mostly not statistically significant.
That suggests that, overall, the 2016 national pre-election polls were generally accurate and unbiased. That year’s state-level polls similarly underestimated Republican support, but here too these biases were generally statistically insignificant. The larger problem — at least for those who wanted to know the outcome in advance — was too few quality statewide polls in key battleground states, compared with previous years.
Nevertheless, the discrepancy between poll projections and the eventual outcome pushed many pollsters to reconsider their methods. Survey researchers scrutinized the 2016 polls and considered an array of factors that potentially contributed to underestimating President Trump’s support. These included: failure to adjust weighting procedures to account for elevated survey participation among college graduates, who disproportionately went for Clinton; possible “shy” Trump voters; people who decided which candidate to support late in the campaign, and disproportionate increases in turnout among Republicans. As a result, many polling firms changed their weighting procedures.
Many hoped these changes would improve accuracy in the 2020 presidential election. Certainly, pollsters accurately took Democratic primary voters’ temperatures; most primary election polls correctly predicted the winner. But that didn’t translate into improved accuracy in the 2020 general election.
