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Why pollsters don't 'weight' surveys for Dem-GOP mix

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September 27, 2012|By James Rainey
  • President Obama and Republican Mitt Romney on the campaign trail. Some Republicans have taken issue with polls in swing states that show negative results for Romney, citing bias; pollsters defend themselves.
President Obama and Republican Mitt Romney on the campaign trail. Some… (Associated Press )

As polls in swing states continue to roll in with mostly negative results for Mitt Romney, some Republicans have declared that the surveys are bogus because they sample too many Democrats.

The issue has become almost as hotly contested as the presidential race itself, with seemingly daily reports from Karl Rove on Fox News on alleged Democratic “over-sampling” and even an alternative website that claims to “unskew” the polls to eliminate the slant that is said to favor President Obama.

Professional pollsters generally have defended the polls and a methodology that frequently “weights” the survey results to make sure they represent the voting population for several factors — such as race, income, gender and educational level — but not for party identification.

They say that to lock in party makeup in the 2012 contest based on what it was in 2008 or 2010 could mean missing the shifting sentiments among the electorate about the Republicans and Democrats.

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“Party ID is not a demographic quality like age, sex, income or education. It’s an attitude,” said Andrew Kohut,  president of the Pew Research Center. “And it’s an attitude that varies with preferences, so generally when a Republican wins you will see a boost in Republican identification and when a Democrat wins you will see a boost in Democratic identification. If you try to standardize the party ID number, you standardize out some of that change.”

Kohut notes, for example, that Pew successfully called the Republican surge in congressional seats in 2010, but would have missed the change if it had insisted on weighting its results to reflect the Democrat’s pronounced party identification advantage after Obama’s 2008 victory.

Even given such shifts, Republican operatives say the percentage of Democrats in some recent state polls simply don’t make sense. A recent New York Times/CBS/Quinnipiac poll in Florida shows 36% of voters ID as Democrat, 27% as Republicans and 33% as independents. The survey showed Obama with a substantial 53% to 44% lead over Romney.

The Tampa Bay Times noted in a column this week that the 6% Democratic ID advantage would be larger than the current voter registration numbers in the state, which show Dems with a 4% edge, and larger than the 3% ID advantage they had over the GOP when Obama won the state in 2008.

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It’s possible that a bombardment of ads, particularly focusing on the GOP’s plan to alter the nature of Medicare, have taken a toll in a state where retirees are a huge voting bloc. Perhaps that has added a couple of ticks to Democratic identification in the Sunshine State.

The Tampa Bay Times column speculates that the gap is not that wide and guesses that  Obama leads but by something closer to the 3.1% RealClearPolitics average of several polls.

Yet the Quinnipiac surveys were among the most accurate in predicting winners in the 2010 midterm election, which went heavily to the Republicans. The head of the survey organization gave the Atlantic online his argument against weighting for party ID.

"If a pollster weights by party ID, they are substituting their own judgment as to what the electorate is going to look like. It's not scientific," said Doug Schwartz, the director of the Quinnipiac University Polling Institute, which also recently published a survey showing Obama up by 10 points in Ohio.

"A good example for why pollsters shouldn't weight by party ID is if you look at the 2008 presidential election and compared it to the 2004 presidential election, there was a 7-point change in the party ID gap," Schwartz told the Atlantic. Dems and GOPers were equally represented in ’04 but Obama’s party had a 7% advantage in ID by the time of the vote in 2008.

"There are more people who want to identify with the Democratic Party right now than the Republican Party," Schwartz said.

Part of what might explain the tempest over the polls is the Republican conviction that Americans would be driven, in big numbers, into the party’s arms in 2012 because of the sputtering economy. Unemployment stays above 8% and GOP registration (or, at least, identification) has to go up; so the thinking went.

Many surveys have shown, instead, that — though voters continue to have deep misgivings about the economy — Americans don’t have a warm feeling for the GOP standard-bearer. If they don’t take to Mitt Romney, they’re less likely to identify themselves with his party.

Still, the party ID battle is far from settled. Changes in sentiment about Obama and Romney, and the parties they head, are likely in the six weeks before election day.

INTERACTIVE: Battleground states map

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