Our turnout model

There’s a big question on top of the standard margin of error in a poll: Who is going to vote? It’s a particularly challenging question this year, since special elections have shown Democrats voting in large numbers.

To estimate the likely electorate, we combine what people say about how likely they are to vote with information about how often they have voted in the past. In previous races, this approach has been more accurate than simply taking people at their word. But there are many other ways to do it.

Assumptions about who is going to vote may be particularly important in this race.

Our poll under different turnout scenarios Who will vote? Est. turnout Our poll result The types of people who voted in 2014 205k Walters +7 People whose voting history suggests they will vote, regardless of what they say 248k Even Our estimate 252k Porter +1 People who say they will vote, adjusted for past levels of truthfulness 268k Porter +3 People who say they are almost certain to vote, and no one else 278k Porter +9 The types of people who voted in 2016 313k Porter +1 Every active registered voter 396k Porter +8

In these scenarios, higher turnout tends to be better for Democrats.