How many Democrats? How many Republicans?

 

Many posts ago I told you that one indication of where an election is likely to go is revealed by the underlying partisan predispositions of the voting public. Rasmussen is one of the few pollsters that periodically polls the public regarding its partisan identification and weights their surveys accordingly. This is important because it allows us to see if the underlying partisan identification among voters is changing across a campaign. Today Rasmussen released their final partisan weighting before the election, and it remains almost unchanged from its previous weighting in October: 39.9% Democrat, 33.4% Republican and 26.76% unaffiliated. This represents an almost miniscule shift in the Republican direction in the last month, but does not eliminate the gains the Democrats made in partisan backing since the fiscal meltdown beginning in late September.  In mid-September, prior to the meltdown, Rasmussen’s surveys indicated 38.7% Democrat, 33.6% Republican and 27.7%. So since the fiscal meltdown, Democrats have gained 1%, Republicans have gained nothing and independents have lost a 1%.  In short, Republicans have lost ground within the electorate during the current campaign. The current partisan distribution is in stark contrast to 2004, when Rasmussen’s November weighting showed an almost evenly divided electorate, with 37.1% Republicans, 38.6% Democrats, and 24.3% independents.  This demonstrates the steep hill McCain has had to climb during this campaign.

So what explains the difference in the Rasmussen and Gallup tracking polls? Rasmussen gives Obama a 5% lead, but Gallup’s traditional likely voter model gives Obama a 10% lead.  What happened is that Gallup changed their estimate of the likely voter turnout on Election Day from 60% to 64%, in response to the early voting, and they are estimating that most of this increased turnout will come from Obama voters.  So it’s not that they are picking up any movement toward Obama – they have simply changed their model’s assumptions.  Rasmussen has not – so it appears they are contradicting one another.  But in fact both Rasmussen and Gallup have Obama getting 51-52% of the vote – they only differ regarding how much McCain will get.

When we look at the daily tracking polls, all of them now have Obama at 50% or higher except for IBD (Obama at 48%) and Zogby (Obama at 49%).  The average for Obama among the daily trackers, including Zogby and IBD, is 50%.  Where the polls differ is in the support for McCain, whose support ranges from 42 to 46%.  This means that McCain is not likely to win this even if he takes the undecideds 5 to 1 – he has to count on some slippage in Obama’s support.

To summarize, everything points to an Obama victory in the popular vote on Tuesday – unless there is some systematic bias in the polls that is overstating Obama’s support and/or understating McCain’s.  Tomorrow I’ll address the much discussed but little understood Bradley effect.  Are polls systematically overstating Obama’s support?

2 comments

  1. I know you regard 538.com with skepticism, but one point I’ve read a lot there is that each poll weights their sample by partisan affiliation differently, with Zogby using an even split between D/R, while others follow the national or state distributions more directly. Any thoughts on this issue in terms of reading the varying polls?

  2. Jason – I should be clear here – when Silver presents numbers, he is usually very reliable and often quite informative. It’s when he shades over into political interpretation that his bias starts showing.

    But you are right – different pollsters use different partisan weightings – I’ve touched on this periodically in my posts. Zogby’s basic rule is to use the partisan weighting from the 2004 election. Rasmussen, in contrast, adjusts their partisan weighting based on polling every month. Other pollsters use different weightings – for an extreme example, look at the Daily Kos. They typically weight their survey to have only 26% Republicans, which is why you can pretty much ignore anything they report. A good illustration of the impact of these assumptions is to compare Gallup’s recent survey results to their earlier results – it appears that Obama has surged in the recent Gallup polls. But in fact what has happened is that they have changed their projections regarding turnout from 60% to 64% with most of the increase projected to be Obama voters. So its not that more people are moving toward Obama – it’s that Gallup is weighting their sample to include more Obama voters.

    That is what makes polling this election so difficult – we are moving into uncharted territory regarding turnout projections, and different pollsters are making different assumptions.

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