Polls predicting the outcome of the 2020 presidential race - and numerous state races as well - suffered from the worst errors in four decades, according to a new survey.
But experts say the reason why is a mystery.
Public opinion surveys significantly overestimated President Joe Biden's margin of victory over Donald Trump, according to a study of 529 national presidential race polls and 1,572 state-level presidential polls conducted by the American Association for Public Opinion Research.
Days after Americans went to the polls, the final results showed Biden winning more than 81 million votes while Trump won just over 74 million.
Projections leading up to the November election overstated Biden's margin over Trump by 3.9 percent in the popular vote and 4.3 percent in state polls.
A poll from YouGov placed Biden a whopping 11 points ahead of Trump just a week before Election Day.
Biden ended up beating Trump in the November election by 4.4 percent of the popular vote.
A study of nearly 3,000 state and national level polls found that most projections significantly underestimated Trump's performance in the 2020 election
Polls conducted in the two weeks before Election Day were off by 5 percentage points on the state level.
Support for Trump exceeded expectations in almost every state by more than three percent on average.
In contrast, support for Biden was projected to be one point higher than he ended up winning.
The same polls were widely criticized in the weeks after the election after Trump outperformed expectations.
A Morning Consult poll out the day before the election showed Biden leading Trump in five battleground states
AAPOR came to its conclusion after examining nearly 3,000 different surveys on the state and national level.
But the task force of 19 election and political science experts is at a loss when it comes to why so many polls underestimated Trump.
'Identifying conclusively why polls overstated the Democratic-Republican margin relative to the certified vote appears to be impossible with the available data,' the report states.
Support for Trump dropped since the start of the coronavirus pandemic in the national Morning Consult poll, but the AAPOR task force hasn't conclusively said why the final results were so different from poll projections
