Pollsters have made two significant changes this year aimed at improving accuracy over 2016.
One is simply conducting more polls, a costly decision but one that may contribute to greater precision overall. From the start of September to last week, RealClearPolitics tracked 105 polls in Pennsylvania, Michigan, Wisconsin and Arizona, nearly double the 54 polls over the same period in 2016 in these states. The number of nonpartisan polls conducted with live telephone interviews — a more expensive but historically more accurate method — grew from 24 in 2016 to 36 in 2020.
In addition, more polls also appear to be weighting samples by educational attainment, something that wasn’t done in 2016 and that the AAPOR’s post-election report found contributed to polls underestimating Trump’s support.
Polls are routinely weighted to match estimates of population demographics including race, age and other factors that are correlated with voting. In 2016, there was an especially strong correlation between education and support for Trump and Clinton in key states, with Trump winning by wide margins among White voters with some college or less. Current polls show that correlation remains strong in this year’s election between Trump and Biden. College graduates have long been more likely to participate in surveys, and states that did not weight samples to correct for that — by weighting down the share of responses from people with degrees to their accurate share of the population — were at greater risk of underestimating Trump’s support.