In the weeks leading up to the 2024 presidential election, Guardian polls showed Kamala Harris winning an incredibly close race. Yet Donald Trump won, showing that his support volume was once again underestimated.
Although Harris won according to Guardian US averages, the final result was within the margin of error for high-quality polls conducted during this election cycle.
With an estimated 99% of votes counted, Guardian national polling averages in the US were three percentage points lower on November 20, 2024, an analysis of the 2024 presidential election results shows.
While this may change as more votes are counted, preliminary results show that polls have underestimated support for Trump for the third election in a row. The Guardian’s US national polling average had Harris at 48% and Trump at 47%, with the end result showing Trump at 50% and Harris at 48%, an error similar to polling errors in previous elections.
Guardian’s US national averages only averaged high-quality polls, but swing state polling averages used every poll collected by 538. Fewer swing state polls are conducted, but they are important because national polls are not indicative of who the will win elections. election, only the level of support at the national level.
According to the US Guardian averages, Trump won four of the seven key swing states and there was a wider spread in accuracy for swing states.
“Especially in swing states, you don’t have a lot of high-quality polling,” said Andy Crosby, an assistant professor of education at the University of California Riverside School of Public Policy.
The averages of the swing state polls were not significantly different, and nationally, the swing state polls were accurate, Crosby said.
“High-quality polls were within the margin of error for many of these critical swing states,” Crosby said.
In the key swing states that the Guardian US tracked, the difference between the polls and the results ranged from a difference of 0 percentage points in Georgia to a difference of 4 percentage points in Arizona.
The Guardian US began tracking national and swing state polls in August, and in the weeks leading up to the presidential election, the 10-day moving averages showed an extremely tight race.
Throughout October 2024, Harris was one to two points above Trump, with the difference falling to one percentage point on October 31, the last day Guardian US averaged state and national polls.
The election results show that the electoral error in the 2024 presidential election is similar to that of previous elections. A 538 analysis of past polling errors found that between 1996 and 2020, polling errors for their averages ranged from 0.1 pp in 2008 to 4.3 pp in 1996. The Guardian’s national polling error was 3 percentage points, meaning the polls in 2024 were no deviation from previous years.
Although the polling averages were close to the final results, the averages all favored Democrats, with Trump doing better than the polling averages expected in every swing state.
This is a recurring pattern in elections where Donald Trump ran for office. Opinion polls underestimated Trump’s performance in 2016, when he defeated Hillary Clinton, and in 2020, even though he lost to Joe Biden.
Although polls were attacked in 2016 for the lack of support for Trump, national polls were accurate, according to the American Association for Public Opinion Research.
“After the 2016 election, there was a lot of effort to do a debrief on what,” Crosby said of the AAPOR report. “There was a lot of inner thinking, like, what are we going to do to address this? The conclusion was largely again: Look, the national polls were accurate.”
Once again, it was issues in the swing state polls that missed the mark.
“We’re seeing this kind of pattern repeating itself in terms of, oh gosh, it’s going to come down to the swing states and we don’t have the data for the swing states,” Crosby said.
The 2020 polls showed the highest polling error in four decades for the popular vote, even though Biden won in line with what the polls expected, according to the 2020 AAPOR report. However, why the polls were off remains a mystery.
“It seems impossible with the available data to conclusively identify why polls overestimate the Democratic-Republican margin over the certified vote,” the report said.
According to experts like Crosby and opinion leaders like Nate Silver, there are several reasons why the polls showed errors in the same direction in three elections.
Random coincidence, the demographics of those responding to polls, the election being extremely close, or even people being reluctant to express their support for Trump to strangers on the phone could all be part of the overall explanation. But Trump won’t run in 2028, so it remains to be seen whether there is some unique aspect of Trump voters that continues to elude pollsters’ ability to gauge his support.
