Poll-based election forecasts were widely maligned after the 2016 election, and with some justification: Donald Trump won the election when the bulk of the polling said he would not. Forecasts based on polls performed well in 2008 and 2012, with several analysts correctly picking the winner in all fifty states in 2012. And yet the same methodology — using statistical models to combine poll results — did not fare nearly so well just four years later in 2016. The accurate performance of these methods in 2008 and 2012 led many analysts of 2016 polling data to incorrectly predict Trump would lose.

With polls currently showing Joe Biden handily leading Donald Trump nationally and in many swing states, this research note:

• reviews the current state of 2020 polls;
• reminds ourselves of the magnitude of the error associated with poll-based forecasts in 2016;
• asks what went “wrong” with the polls in 2016;
• applies those “lessons learned” to analysis of 2020 election polling.