Exit Polls & Early Voting
Thanks for the comment, Valerie. I should have mentioned this in the story. You’re right, early voting has really revolutionized everything, and I think the day is coming when we will all vote early.
But to answer your question, this year, exit pollsters dealt with early voting by doing telephone surveys of early voters in 18 states before the election. The phone survey had its own problems (it only included landline phones, for example), but it was in other ways easier to control than physically surveying people at polling places. The data was then merged with the data from the exit polls.
For more on early voting and polling, check out this helpful New York Times piece.
For more on polling in general (something all of us could stand to be more literate in, given the way the world works today), I strongly recommend Pollster.com. Mark Blumenthal is a particularly invaluable explainer.