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Tuesday, September 9, 2008

Major issues with SurveyUSA's North Carolina Polling Sample

SurveyUSA released a rather shocking poll today showing John McCain leading Barack Obama 58-38 in North Carolina, up from 4 points in the August poll.

They also recorded an 11 point gain for Republican Pat McCrory in the Governor's race, and a 3-point gain for Elizabeth Dole in the Senate race.

A lot of people might have thought, "Hey, maybe we messed something up here." Not SurveyUSA, though.

Republican John McCain suddenly and breathtakingly surges to a 20-point win over Democrat Barack Obama, 58% to 38%, according to this latest exclusive SurveyUSA election poll conducted for WTVD-TV. In 3 previous SurveyUSA NC tracking polls, McCain had led by 8, 5, and 4 points. Today: 20. McCain has gained ground in every demographic group.


Now, first of all, their claim is false. Obama led 71-25 among Democrats in August's poll; today, he leads 74-23.

That fact led me to look at the crosstabs for party affiliation; 41% Republican, 40% Democratic. I wondered if they were going by stated party affiliation or registered party affiliation; those numbers may be accurate for stated affiliation but they are way off for registered party affiliation.

So I took a look at the other 3 months polls that they've done, and it's clear: they've been polling by registered party affiliation.

In August: 46% Democratic, 33% Republican

In July: 45% Democratic, 37% Republican

In May: 49 % Democratic, 33% Republican

The Democratic registration edge in all 3 of the previous polls is within 4 points of the Democratic registration edge among registered voters in North Carolina.

Currently, 45.3% of North Carolina's registered voters are Democrats, 32.7% are Republicans (12.6% edge). This is a gain of 2 points for Democrats since January, when 44.8% were Democrats and 34.2% were Republicans (10.6 point edge)

My point is that this a really, really awful sample of voters. If you take the crosstab numbers by party registration for this poll and adjust them to reflect last month's poll, you get the following:

McCain 51, Obama 42 (still a 5 point gain; not insubstantial but not crazy either)

Hagan 44, Dole 42 (a 7 point gain for Hagan, in line with other polls we've seen from the state)

Perdue 45, McCrory 44 (a 2 point gain for McCrory, within the margin of error)

The point being: McCain may well be safe in North Carolina (and the Obama campaign may realize it as they've cut back resources there), but Dole isn't and Perdue's got a fighting choice.

Or rather, that's what this poll says.

1 comment:

researchrants said...

SurveyUSA pretty famously doesn't do any party affiliation weighting; they ask the question and report the results. If it's been close to state registration figures in past months, that's great, but it's really a coincidence.

I'm not surprised to see a jump in GOP party ID right now; party ID does tend to move around quite a bit, depending on exactly how it's asked. PPP is going to have numbers out tomorrow, according to their blog -- it'll be interesting to see what they show.