That's particularly true of polls taken during, and just after, the nominating conventions. This year's prize goes to CNN and USA Today for ordering up a one-night Gallup poll after Al Gore's choice of Senator Joe Lieberman as his running mate. Similarly, Newsweek and others that polled just after each of the conventions reported dizzying shifts in opinion this year, as the unstable opinions of voters with low conviction were buffeted by news events. These polls seem almost calculated to portray instability in public opinion rather than look at the underlying factors that make many voters unsure of their choice. The bounce is real, but often short-lived, and always confusing to audiences.
People throw their hands up and dismiss the mystifying patterns in the polls, with good reason.
There are legitimate debates about when and how to distinguish between eligible voters and those most likely to vote. The samples are routinely corrected using demographic census data on sex, age, race, education, and other factors to help overcome sampling imbalances. The problem is that party affiliation is an attitude, not a stable characteristic such as age or educational attainment. Furthermore, self-identification with the political parties changes over the course of campaigns, especially when one candidate has a big lead. There has always been plenty of room for different approaches in polling, but personal judgments about the composition of the sample have not been part of the equation.