Since Joe Biden's lead in national polls remained stable throughout the summer, why have betting markets now moved dramatically towards Donald Trump and voters are still sceptical of a victory for the Democratic nominee? https://www.ft.com/content/b3297609-e63b-4161-8287-7ab1179d0c40

Many people are blaming state polls, which show that Joe Biden is actually doing worse at this point in the race than Hillary Clinton was in 2016, especially in swing states. But here's why it’s hard to compare 2016 with 2020 state polls: https://www.ft.com/content/b3297609-e63b-4161-8287-7ab1179d0c40

In the states where it mattered most, 2016 polls underestimated Donald Trump’s support, failing to adjust samples by education, meaning they polled too many highly-educated voters. Many pollsters have since corrected this mistake https://www.ft.com/content/b3297609-e63b-4161-8287-7ab1179d0c40

Education levels didn't used to matter too much in polls, but in 2016 it was arguably the most important demographic factor determining who voters — particularly white ones — would pick https://www.ft.com/content/b3297609-e63b-4161-8287-7ab1179d0c40

Education alone doesn't explain the polling deficiencies in the run up to the last election. There were lots of undecided voters who disliked both candidates but shifted to Donald Trump in the final week before the election https://www.ft.com/content/b3297609-e63b-4161-8287-7ab1179d0c40

This year, there is less potential for late-deciders to affect the race in either direction. Polls suggest there are far fewer undecided voters than there were in 2016 — and the ones who don't know who to vote for are leaning to Joe Biden https://www.ft.com/content/b3297609-e63b-4161-8287-7ab1179d0c40

Many of the issues that affected election polling in 2016 remain. Reputable pollsters in key states are grappling with lower budgets and increased costs from methodological changes, which means high-quality state polls are still too infrequent https://www.ft.com/content/b3297609-e63b-4161-8287-7ab1179d0c40