I was just wondering

 

All these political polls and early voting.  I was just wondering how the polls account for people who have already voted.  Polls are predictions of what people are going to do.  If people in the sample have already done what they’re sampling for, then it’s no longer a poll of what people are going to do, it’s a report on what people have done.  But if the pollsters don’t include people who have already voted in their sample, then they’re sampling something other than the general population.  The people who have already made up their minds and voted might be different from the people who have not yet been motivated to vote, or are still undecided.

 

Pollsters have to be clever enough to quantify what they think has already happened, combine that with their conclusions about what they think has yet to happen, and come up with a projection of the combined results.