There are two parts to a polling prediction: predicting how each demographic is going to vote, and predicting how many of each group will show up to vote. I bel

There are two parts to a polling prediction: predicting how each demographic is going to vote, and predicting how many of each group will show up to vote. I believe the weighting refers to the second part of the process. It appears that the groups more likely to vote for Hillary stayed home on Tuesday more than anybody predicted. There's an article I read within the last couple of days that goes into detail about the weighting process, but I couldn't find it again.