UPDATE 8/21: Rasmussen has a new poll showing Doyle at 49, Green at 41. Blogger is refusing to upload my new graphs, but as soon as it feels better I'll update the graphs here as well. Graphs are now updated.
Two new polls out on the Wisconsin Governor's race tell much the same old conflicting story. (See here and here for previous tellings of this tale.) A WISC-TV/Research2000 poll conducted 8/14-16/06 found incumbent Democrat Jim Doyle with a 48%-38% lead over Republican challenger Mark Green. Green is the incumbent member of the U.S. House from the 8th Congressional district (Green Bay.) But a Strategic Vision survey conducted 8/11-13/06 found a miniscule Doyle lead, 45%-44%. The Strategic Vision poll is exactly in line with their past polling showing the race as a virtual dead heat, with a very slight Doyle advantage. The WISC/Research 2000 poll is in line with other statewide polling that has consistently found a substantial Doyle lead, but which has also shown a slow but steady rise in Green's support. The problem, of course, is which poll to believe, or at least how to understand why they are different.
The top figure shows the trends for Mark Green with Doyle's support as the gray dots. Doyle's polling is quite consistent across all the polls, with support in the mid-to-upper 40s but consistently falling short of the 50% point. Green on the other hand varies widely across polls, with a slow upward trend for the "green" line polls but largely flat (though higher) in the other organizations' polling.
An alternative look is given in the graph below, which plots the margin between Doyle and Green in each poll. Strategic Vision and Zogby's Internet based polls find little or no trend, while Rasmussen's "Robo-poll" finds a larger margin, but also no trend. The other polls find a small downward trend and a larger Doyle lead.
(Graph updated 8/21 with new Rasmussen poll.)
So why the differences? One reasonable theory now seems less plausible. The "green line" polls from WPRI, WPR, UWM and Badger were samples of adults rather than "likely voters". That made for a nice story-- adult samples include more people who are less interested in politics and therefore know the least about any challenger. The result would be lower support for the lesser known candidate. In contrast Strategic Vision samples "likely voters" whose greater interest and involvement would increase their knowledge of the challenger, making him appear more competitive in their samples.
The problem is that the new WISC/Research2000 poll is also of "likely voters", so the 10 point gap there can't be explained as due to the sample population vs the population producing the 1 point gap in Strategic Vision. Now all firms differ in how they select "likely voters", and they rarely explain their methods (often they are considered proprietary) so there may still be some difference in method here. Still, this is a large and persistent gap.
A further complication is the fact that WISC/Research2000 DOES line up with the previous samples of adults. Why doesn't the more selective likely voter sample produce at least some advantage for Mark Green? (Any comparison across survey organizations is fraught with peril since they differ in many ways. Still we'd expect a systematic difference between adults and likely voters to stand out more.) If we must strain for some explanation of this, one possibility is that the campaign remains low key enough that even likely voters have not yet started paying attention. Us junkies are certainly attending to every word, and streaming the commercials as soon as they come up on the candidates' websites, but "normal" people may still not be that aware of the campaign, even among those regular voters who are captured in the "likely" voter sample. (Of course there is a good deal of post-hoc rationalization there, when the obvious prediction should be that Mark Green does better in LV rather than Adult samples, so make of this story what you will.)
If we accept for the moment that the issue is NOT the sample population, then what might account for the Strategic Vision difference? Democrats have been critical of the Strategic Vision surveys, pointing out that Strategic Vision is a Republican firm that does these statewide "free" surveys as a marketing tool. But I think Democrats are wrong to claim that Strategic Vision is a "bad" pollster. I tracked 1486 statewide polls of the 2004 presidential race, of which Strategic Vision did 196. The Strategic Vision polls average error overstated the Bush margin by 1.2%. The 1290 non-Strategic Vision polls overstated KERRY's margin by 1.3%. Further, the variability of the errors was a bit smaller for Strategic Vision than for all the other polls combined. (That is a little unfair to the other pollsters because it mixes many organizations while comparing to a single survey "house." Since pollsters differ, that increases the variation due to pollster in the 1290 non-Strategic Vision polls.) So the bottom line is that Strategic Vision does not appear, based on their track record in 2004, to be noticably biased compared to others. And they did err in the correct direction of the winner in 2004, while others erred in the direction of the loser.
So what else might explain the differences here? One possibility is the order of the questionnaires. WISC/Research2000 appears to have asked Doyle Job, Doyle and Green favorability and then vote. getting right to the point. In contrast, the Strategic Vision polls have always opened with a lengthy battery of national questions. In the most recent poll they have 11 questions before asking Doyle job approval, legislature job approval and then vote. The 11 opening questions include Bush job overall, on the economy, war, terror and immigration, whether Bush is a "Reagan conservative", amnesty for illegals, building a wall on the border, whether Roe v. Wade should be overturned, whether we should withdraw from Iraq within 6 months, and whether there will be a terrorist attack in the next six months! That's a LOT to think about before getting to the Governor's questions. While they mostly don't deal with state politics, this series seems likely to raise people's partisan and ideological awareness and might well then structure responses more along partisan lines. That could raise Green's votes among Republicans who aren't yet paying attention, but whose Republican loyalties have been activated by the opening 11 questions. In contrast, the WISC poll with little introduction would do less to get people thinking along partisan lines.
Since Strategic Vision always has had this lengthy opening section prior to the state race questions we can't know if the order of questions really produces this effect or not. (If they'd randomize the order for us once we could find out!) But since the sample population doesn't seem to be the key variable, survey question order is the next most likely suspect.
It is great to see WISC sponsoring Research2000 polling. That brings a new and independent pollster to the table, which provides crucial information about why the polls differ. At least now we know it isn't simply the adult vs likely voter difference in the samples.
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