Infamously, polls in 2016 and 2020 systematically underestimated Mr Trump’s vote, especially in battleground states. After the 2016 election, the post mortem conducted by AAPOR, a professional organisation of pollsters, pointed to a late swing towards the Republican nominee and overrepresentation of graduates in poll samples. Most firms began to weight their samples to do a better job of reflecting the education profile of voters.
In 2020 the underestimation of Mr Trump was repeated for different reasons. This time AAPOR identified non-response bias—Republican voters were less likely to respond to pollsters. One theory is that they were less likely to be at home during the covid-19 pandemic (twiddling their thumbs and responding to surveys). Another is that Republican voters distrust pollsters, which discourages them from answering surveys.
Since 2020 pollsters have been at pains to reach a representative sample. They have experimented with recruitment that appeals to certain sections of society (postcards plastered with patriotic imagery, for example) and new modes, such as text messages. It is anyone’s guess whether this will be enough to account for the Democratic bias in response rates or whether supporters of Mr Trump are still reluctant to answer polls. If the errors seen in 2020 or 2016 are repeated even to a small degree that would be disastrous for Ms Harris—she could lose all seven swing states.
The last Campaign Calculus to print before the election [😱] is on polling errors—all seven swing states are well within a normal polling error of flipping! https://t.co/vhMC84TtFE pic.twitter.com/e2JFce3u16
— Owen Winter (@OwenWntr) October 29, 2024