We have devoted much attention recently to the flood of new national surveys showing small declines in the Bush job approval rating and modest Democratic gains on the generic House ballot question since mid-September. Until today, I had not looked closely at levels of party identification reported on those surveys. It turns out those have also trended Democratic recently, a finding that may explain some of the apparent "house effect" differences among statewide pollsters over the last few days.
The debate over weighting surveys by party identification has been a focus of this blog since its inception. My posts on the subject from 2004 and beyond are worth reviewing but the gist is this: Pollsters typically ask respondents some variant of a question asking whether they consider themselves "a Democrat, a Republican or an independent?" The so called "Party ID" question has been asked, examined and studied for more than 50 years, and an ongoing debate exists about whether to weight (or statistically adjust) survey results by party.
The crux of the debate is whether party identification is more like a fixed demographic characteristic (such as gender or race) or more like an attitude that can change with the prevailing political winds. For most adults, party identification does appear to be highly stable, changing rarely if ever. The problem is that some small portion of voters (perhaps 10% or 15%) appear willing to jump back and forth -- usually between one of the parties and the independent category -- depending on the wording of the question, its position in the survey, how hard the interviewer pushes for an answer, or, in some cases, what has been happening in the news.
Those who argue for weighting by party say that the real trends tend to be slow and gradual and that party weights can adjust dynamically over time to accommodate these slow moving trends (see also the party weighting page maintained by Prof. Alan Reifman). Those who argue against party weighting (a class that includes most of the national media pollsters) worry that such an approach will suppress real but short-term changes that sometimes occur in reaction to news events (such as the period just after the 9/11 attacks or the period just after the 2004 Republican convention).
A look at the party identification data from the recent surveys suggests we may be in the midst of another such short term change. The table that follows shows party identification results for six national surveys conducted before and after the resignation of Congressman Mark Foley. Five of six show some Democratic gain in party identification:
This change may also explain the wide divergence in results reported by the two automated pollsters in two nearly simultaneous surveys conducted this week in Missouri and Ohio. In both states, SurveyUSA showed the Democratic candidates with significantly greater leads (+14 in Ohio and +8 in Missouri) than Rasmussen (+6 in Ohio and -1 in Missouri). While both pollsters use the automated "interactive voice response" (IVR) methodology, Rasmussen weights by party and SurveyUSA does not. Moreover, the most recent SurveyUSA samples have grown more Democratic since August.
Does this shift in party identification represent a real shift in attitudes among the population of adults or registered voters or does it reflect some short enthusiasm among Democrats to be interviewed? Is the change a momentary spike or will it persist until Election Day? These are the questions that professional pollsters are mulling over right now, and the answers are not obvious. We will just have to wait and see (no pun intended).