What’s confusing here, I suspect, is use of the word “delta,” which in this context means “change in” or “difference of”. What Nate Silver is saying in his geekish way (click on the link after his name in red) is that between the pre-election polling and the actual election result there was a swing of about 14% in the Republican’s favor. It would be odd, to say the least, for pre-election polls to be that far off. Something smells fishy, and Silver floats several hypotheses as to what might have gone on.

Hey, Ms. Giambruni, great to see you posting here! Any time.