by Jerome Armstrong, Sat Sep 11, 2004 at 11:23:44 AM EDT
1. As an observer of party identification tallies day after day on our election surveys, it's clear that we're not measuring a constant factor. It varies day by day, week by week.
2. Why does it vary? Most polls place the party ID question near the end of the questionnaire, so that it does not interact or contaminate the horserace measure and any other head-to-head candidate comparisons. The horserace always takes priority, since that's the topline number we report. As a result, respondents may tend to bring their party ID in line with their partisan choice, particularly after having gone through an extensive battery of election items. It's simply "cognitive consistency." Hence, a Bush surge, for example, might elevate the number of voters later in the survey identifying themselves as Republicans.
3. Since party ID is a "variable" and not an enduring constant, as is age or gender, it varies!
4. Voting behavior literature (Campbell, Converse, Miller and Stokes, The American Voter, for example), used to posit party ID as anchoring partisan choice, as if it were a constant. It's likely that party ID was a more enduring "constant" in the 1950's, but, that was then, and this is now! Voters are just not as tied to party as in the past. Let's get over this likely out of date notion that party ID is a constant that anchors the vote. The causal arrows here are unclear, that is, what influences what.
5. Hence, weighting by party ID, and its party ID, not party registration, can seriously distort the horserace data. Weighting by party ID would damp down the Bush surge over the past few weeks. Yes, there may be some "at home" selection bias when we interview during party convention periods. However, not all that many folks watch the conventions and the networks provide little convention coverage.
Finally, my choice, and the choice of most the major media polls, is to weight by factors that we know are real, such as age, gender, region, education, number of adults in household, number of voice phone lines, etc. While you can argue about the reliability of Census data, I'll place my bets with the Census rather than party ID.
David Moore has a good discussion of this issue as well on the Gallup web site.
That's the short version of my views. I really do believe that we need to put this issue to rest and stop pretending that there's legitimacy to party ID weighting. I look forward to further comment!
It can't be ignored that media vehicles such as Newsweek and Time live for things like "the Bush surge", as Mark puts it. They want a horserace that makes news & sells magazines. Regardless of the argument, SRBI's treatment of party ID as being somewhat fluid (and therefore not a factor to weight for) satisfys that need. Rasmussen 2004, Zogby, and SUSA might not be as flashy in their ups and downs, but their accuracy is just fine, or better, and arguably due to their Party ID weighting. I'll put the responses in the extended entry.