July 19 (UPI) -- A national survey of over 2,000 polls nationwide has found the 2020 presidential polls to be the least accurate in 40 years while the state polls were the worst in at least two decades.
An American Association for Public Opinion Research review released Monday found that pollsters overstated Biden's lead over former President Donald Trump by 3.9% nationwide and 4.3% on the state level.
Polling numbers for Biden also were off by about 1%. The organization was unable to readily explain the disparity that occurred across a variety of polls.
"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, according to the Washington Post.
In all, the association election task force reviewed 2,858 polls to reach its determination.
"We could rule some things out, but it's hard to prove beyond a certainty what happened," said Vanderbilt University professor Josh Clinton, who chaired the association's 2020 election task force.
"Based on what we know about polling, what we know about politics, we have some good prime suspects as to what may be going on."
The organization said the most likely answer is a segment of the Republican voting base is less likely to engage in polling.
"It seems plausible to the task force that, perhaps, the Republicans who are participating in our polls are different from those who are supporting Republican candidates who aren't participating in our polls," Clinton said. "But how do you prove that?"
The polls saw the worst performances since 1980.
In a visit to Philadelphia last week, Biden called allegations of election fraud a "big lie" and struck out against states that have passed sweeping election laws.