The US presidential election might be closer than the polls suggest (if we can trust them this time)
- Written by Simon Jackman, Chief Executive Officer, US Studies Centre, University of Sydney
With less than two months until the US presidential election, Democratic nominee Joe Biden leads incumbent Donald Trump in the bulk of opinion polls.
But poll-based election forecasts have proved problematic before. The polls were widely maligned after the 2016 election because Trump won the election when the majority of the polling said he would not.
What went wrong with the polls in 2016? And is polling to be believed this time around, or like in 2016, are the polls substantially underestimating Trump’s support?
Read more: How did we get the result of the US election so wrong?
Swing states decide US presidential elections
US presidential elections are two-stage, state-by-state contests.
States are allocated delegates roughly proportional to their populations, with 538 delegates in total. The votes of Americans then decide who wins the delegates in the Electoral College.
In almost all states, the candidate who has the highest vote total takes all the delegates for that state. The candidate who wins a majority (270 or more) of the Electoral College wins the election.
Mary Altaffer/APFor the fifth time in American history, the 2016 election produced a mismatch between the national popular vote and the Electoral College outcome. Hillary Clinton, the Democratic candidate, won nearly 2.9 million more votes than Trump, yet still lost the election.
Trump won states efficiently, by razor-thin margins in some cases, converting 46% of all votes cast into 56.5% of the Electoral College. Conversely, Clinton’s huge popular vote tally was concentrated in big states such as California and New York.
For this reason, election analysts focus less on national polls and more on polls from “swing states”.
These are states that have swung between the parties in recent presidential elections (for example, Michigan, Wisconsin, Pennsylvania, Florida and North Carolina), or could be on the verge of swinging (Arizona, Texas, Georgia and Minnesota).
These states — even as few as two or three of them — will decide the 2020 election.
State polls currently point to a Biden win
As part of a large research project at the United States Studies Centre, we have compiled data from polling averages in all the swing states going back to 120 days before the election and compared them to the same time periods in 2016. Our goal was to provide a key point of reference to more correctly read the polls in 2020.
The charts for all swing states can be found here.
Our research shows Biden currently has poll leads in several states that went for Barack Obama in 2008 and/or 2012 and then swung to Trump in 2016, such as Florida, Michigan, North Carolina, Pennsylvania and Wisconsin. These five states are worth 90 Electoral College votes.
Biden also leads the polls in consistently Republican-voting Arizona (11 electoral votes).
So, if we take recent polls in these states at face value, then Trump would lose 101 of the Electoral College votes he won in 2016 and be soundly defeated.
Tannen Maury/EPAWhy did state polls perform poorly in 2016?
But state polls were heavily criticised in 2016 for underestimating Trump’s support, as these charts in our research highlight.
The final poll averages in 2016 underestimated Trump’s margin over Clinton by more than five points in several swing states: North Carolina (5.3), Iowa (5.7), Minnesota (5.7), Ohio (6.9) and Wisconsin (7.2). This is calculated by taking the difference between the official election result and the average of the polls on election eve.
A review of 2016 polling by the American Association of Public Opinion Research examined a number of hypotheses about the bias of state-level polls in 2016.
Two predominant factors made the difference:
1. An unusually large number of late-deciders strongly favoured Trump
The number of “undecideds” in 2016 was more than double that in prior elections. Of these, a disproportionate number voted for Trump.
But 2020 polling to date reveals far fewer undecided voters, suggesting this source of poll error will not be as large in this year’s election.
Authors: Simon Jackman, Chief Executive Officer, US Studies Centre, University of Sydney