The big poll release of the day is the new IA/NH/SC/national survey from the Associated Press and the Pew Research Center. Most that have posted results so far have noted an unusually long field period for the statewide surveys: 19 days from November 7 to November 25.
One reason for the longer field period is that the Pew Center, like the ABC/Washington Post surveys, but unlike the Register/Selzer and CBS News surveys, sample with a random digit dial methodology that begins with all adults in Iowa rather than all registered voters. As such, it requires more dialing.
However, the long field period and delayed release make it less than comparable to the new Des Moines Register survey that was released over the weekend and fielded from November 25-28. I asked Scott Keeter, Pew's director of survey research, about the rationale for their longer field period, and he responded via email:
The longer field period was a result of the fact that the purpose of the study was an in-depth look at the issues and voter considerations across three states, and not just the horse race. Long interview, two races, three states - the practical impact was a long field period.
As it happens, Gary Langer, polling director at ABC News, concluded his blog this morning about what constitutes a statistically significant "lead" in Iowa with a very similar point:
All this underscores one of the fundamental points about pre-election polls: They are estimates. Even with good-quality methodology, the notion of pinpoint accuracy is a myth. And the reason we do them is not simply to try to puzzle out who's ahead – but to understand how and why the voters are coming to their choices.
I'm curious to hear from our readers: Which is more important to you in the pre-election polls you follow: Their ability to accurately estimate who is ahead or how well they help you understand how and why the voters are coming to their choices?