Likely Voter Screens
How pollsters decide who counts as a 'likely voter' and why this judgment call is one of the most consequential decisions in polling.
The Turnout Problem
Not everyone who is registered to vote actually votes. In US presidential elections, turnout runs around 60-67% of eligible adults (2020 reached about 66%, the highest in over a century). In midterms it drops to roughly 40-50%, though 2018 spiked to about 50%. A poll of all registered voters includes millions of people who will not show up on Election Day, and their preferences may differ systematically from those who do vote.
Likely voter models attempt to filter the sample to include only people who will actually cast ballots. Gallup's traditional screen asks a series of questions: Do you know where your polling place is? Have you voted in past elections? How much thought have you given to the election? How certain are you that you will vote? Based on the answers, each respondent gets a 'likelihood score,' and only those above a threshold are included in the likely voter results.
