Public Opinion Watch: Labor Day Leads

By Ruy Teixeira, The Center for American Progress and The Century Foundation. Posted September 16, 2004.

From the Center for American Progress and The Century Foundation:

In this edition of Public Opinion Watch:

(covering polls and related articles from the week of September 6-12, 2004)

• Why the Race Is a Lot Closer Than People Think
• Labor Day Leads and Possible Election Outcomes This Year

Why the Race Is a Lot Closer Than People Think

Is Bush ahead by a little or a lot? Is it close to a tie ball game or has Bush surged to a commanding lead?

The conventional wisdom inclines to the latter not the former. The reason has a great deal to do with two persistent problems with contemporary polls that – at least at this point in time – tend to considerably inflate Bush's apparent lead. But once you dissect the available data with these problems in mind, a truer picture of the race comes into focus which suggests that the race continues to be very close.

The two problems are: (1) samples that have an unrealistic number of Republican identifiers and hence tend to favor Bush; and (2) the widespread and highly questionable practice of using likely voters (LVs) instead of registered voters (RVs) to measure voter sentiment this far before the election.

First, the issue of partisan distribution in samples. Lately, and very suddenly, many polls have been turning up more Republican identifiers than Democratic identifiers in their samples – in some cases, many more (as high as a nine- to ten-point Republican advantage).

How realistic is it to be suddenly turning up a Republican lead on party identification, much less a large one? Not very. The weight of the academic evidence is that, while the distribution of party identification among voters can and does change over time, it changes slowly, not in big lurches from week to week.

And the weight of the empirical evidence is that the distribution of party identification among voters has favored and continues to favor the Democrats. In 2000, the exit polls showed Democrats with a four-point advantage over Republicans. In 1996, it was also five points; in 1996, it was three points and in 1988 it was also three points.

The data also indicate that there were two shifts in party identification over the 2001-2004 period which largely canceled each other out. The first shift, in the period after September 11, shaved several points off the Democrats' lead and brought the Republicans close to even (but never ahead) in party identification. The second shift took place in late 2003 and 2004 and reconstituted the Democrats' lead on party identiifcation to about four points, exactly where it was in the 2000 election according to the exit polls (see this useful study "Democrats Gain Edge in Party Identification" by the Pew Research Center for more details).

But if the party identification distribution is fairly stable and tends to change rather slowly, why would polls suddenly be turning up unrealistically high numbers of Republican identifiers? The best explanation, in my view, is that when the political situation jazzes up supporters of one party, they are more likely to want to participate in a public opinion telephone poll and express their views. An increased rate of interview acceptance by that party's supporters would then skew the sample toward that party without the underlying distribution having changed very much, if at all.

In this case, the Republican convention, coming on the heels of the Swift Boat controversy, may have helped raise political enthusiasm among Republican partisans, leading to more interview acceptances and a disproportionate number of Republicans in recent samples.

But whatever the explanation for the disproportionate number of Republicans in recent samples, if those numbers are unrealistic, they are skewing reported horse race results toward Bush. What, if anything, should be done about this?

One possible solution is to weight poll results by a more reasonable distribution of party identification. The issue of whether to use this approach to the problem is well-summarized by Alan Reifman in his invaluable essay "Weighting Pre-Election Polls for Party Composition: Should Pollsters Do It or Not?" on his website.

As Reifman puts it:

One factor (among many) that may contribute to discrepancies between different outfits' polls in their Bush-Kerry margins... is polling firms' different philosophies as to whether it's advisable to mathematically adjust their samples – after all the interviews have been completed – to make the percentages of D's and R's in their survey sample match the partisan composition that is likely to be evident at the polls on Election Day. The latter can be estimated from exit polls from previous elections, party registration figures (in states where citizens declare a party ID when registering to vote), and surveys.

Ruy Teixeira is a senior fellow at the Center for American Progress and The Century Foundation.

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