Caught just a piece of a news story on the radio a couple of days ago, where they were talking about the difficulties pollsters face trying to get meaningful projections in this close US presidential race. One pollster was saying that he knew of cases where two polls differed by 15 points in the same state, and he seemed to be implying that was connected to the closeness of the race.
This started me wondering what sort of model could explain that.
We're trying to estimate p = the fraction of voters who will vote for Gore. We do this by measuring p-hat, a fraction of people polled who say they'll vote for Gore. Mostly I guess p-hat is assumed to be normal with mean p and variance depending on sample size.
Obviously the sample has to be truly random and unbiased in some sense for this to work, and presumably the polling companies have techniques they use to try to eliminate bias. This guy seemed to be implying that the nature of the race could either be introducing biases, or increasing the variance of p-hat in some other way.