About that Gallup poll

The most recent Gallup Daily Tracking polls have Mitt Romney up by 6 or points.  When I saw that I almost had a heart attack!  I mean how can that be when President Obama has a lead in all those individual state polls.  Then last night I read Nate Silver’s FiveThirtyEight blog post Gallup vs. the World and I calmed down.  I know that Romney supports are probably convinced that Nate manipulates everything so that Obama comes out ahead, but somehow I doubt that and you might want to actually read the post.  Silver begins

The Gallup national tracking poll now shows a very strong lead for Mitt Romney. As of Wednesday, he was ahead by six points among likely voters. Mr. Romney’s advantage grew further, to seven points, when Gallup updated its numbers on Thursday afternoon.

The Gallup poll is accounted for in the forecast model, along with all other state and national surveys.

However, its results are deeply inconsistent with the results that other polling firms are showing in the presidential race, and the Gallup poll has a history of performing very poorly when that is the case.

Other national polls show a race that is roughly tied on average, while state polls continue to indicate a narrow advantage of about two points for President Obama in tipping-point states like Ohio. The forecast has Mr. Obama as a narrow favorite in the election largely on the basis of the state polls. (You can read my thoughts here on the challenge of reconciling state and national poll data.)

Our database contains records from 136 distinct pollsters that have released at least one state or national survey at some point in this election cycle. Of those, 53 are active enough to have issued at least one survey since Oct. 1.

With so much data to sort through, it will usually be a counterproductive use of one’s time to get overly attached to the results of any one particular poll. Whether you look at the relatively simple averaging methods used by Web sites like Real Clear Politics, or the more involved techniques in the FiveThirtyEight forecast, the Gallup national tracking poll constitutes a relatively small part of the polling landscape.

After a lengthy explanation of how the data is used (I have to say it is long, but readable) Silver says

Over all, the Gallup daily tracking poll accounts for only about 3 percent of the weight [for the FiveThirtyEight calculation] in this stage of the calculation. The national tracking polls collectively, including Gallup, account for only about 10 percent of it. Most of the weight, instead, is given to the state polls.

Silver also recounts the history of the Gallup tracking polls (they have often missed the mark) and concludes

It’s not clear what causes such large swings, although Gallup’s likely voter model may have something to do with it.

Even its registered voter numbers can be volatile, however. In early September of this year, after the Democratic convention, Gallup had Mr. Obama’s lead among registered voters going from seven points to zero points over the course of a week — and then reverting to six points just as quickly. Most other polling firms showed a roughly steady race during this time period.

Because Gallup’s polls usually take large sample sizes, statistical variance alone probably cannot account these sorts of shifts. It seems to be an endemic issue with their methodology.

To be clear, I would not recommend that you literally just disregard the Gallup poll. You should consider it — but consider it in context.

The context is that its most recent results differ substantially from the dozens of other state and national polls about the campaign. It’s much more likely that Gallup is wrong and everyone else is right than the other way around.

Then this afternoon my other favorite wonk, Ezra Klein, also weighed in.

According to Real Clear Politics, Mitt Romney is, on average, up by one point in the polls. According to both Nate Silver and InTrade, President Obama has a better-than-60-percent chance of winning the election. I think it’s fair to say that the election is, for the moment, close.

But not according to Gallup. Their seven-day tracking poll shows Romney up by seven points — yes, seven — with likely voters. But he’s only up by one point with registered voters.

It gets weirder: Dig into the poll, and you’ll find that in the most recent internals they’ve put on their Web site  — which track from 10/9-10/15  — Obama is winning the West (+6), the East (+4), and the Midwest (+4). The only region he’s losing is the South. But he’s losing the South, among likely voters, by 22 points. That’s enough, in Gallup’s poll, for him to be behind in the national vote. But it’s hard to see how that puts him behind in the electoral college.

If Gallup is right, then that looks to me like we’re headed for an electoral college/popular vote split. Last night, I spoke with Frank Newport, editor-in-chief of Gallup, to ask him if I was missing something. He said I wasn’t. “That’s certainly what it looks like,” he says.

But Newport was cautious in interpreting his numbers. Gallup’s poll cheered Romney supporters because it showed Romney gaining ground even after the second debate. But Newport didn’t see it like that. Remember, he warned, it’s a seven-day poll. “I think we’re still seeing leftover positive support for Romney and I don’t think we’re seeing impact yet from the second debate,” he says.

It turns out the Gallup’s likely voter model includes a measure of enthusiasm which might explain why the large swings and the differences from the other polls.  Nate Silver is right:  it is the likely voter model.  He is probably also right when he said on the Daily Show that we tend to follow polls much too obsessively.  But I can’t help myself.

And if you support Obama you can take comfort in the figures posted late last night on FiveThirtyEight:  Obama 291.6 electoral votes with a 70.6 chance of winning.

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