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Aug. 25: An Above-Average ‘Likely Voter Gap’ for Romney

CNN’s latest national poll, released on Friday, contained a mix of good, bad and indifferent news for each candidate.

The good news for Barack Obama? Among registered voters, he led Mitt Romney by nine percentage points, with 52 percent of the vote to Mr. Romney’s 43 percent.

However, Mr. Obama led by just two percentage points, 49 to 47, when CNN applied its likely voter screen to the survey. This is the first time this year that CNN has reported likely voter results.

Holding a two-point lead among likely voters is not an especially bad (or good) number for Mr. Obama, since it is highly consistent with the way that our forecast sees the overall race right now.

What’s worrisome for him, rather, is the large gap in the poll — seven points — between the likely voter and registered voter results.

In our forecast, we use cases like these, in which pollsters report both sets of results, to help calibrate our likely voter adjustment. It is typical for likely voter polls to show more favorable results for Republicans than registered voter ones, and so our adjustment shifts registered voter polls toward Mr. Romney before incorporating them into our averages.

But in past presidential elections, the difference has been relatively small — favoring the Republican candidate by about 1.5 percentage points, on average. (The gap can vary more in midterm election years, when turnout is lower.)

This year, however, most of the polls to report both sets of results have shown a larger gap than that. The seven-point difference that CNN had is not typical. But we’ve been tracking these results whenever state and national polls report them, and the median difference between registered voter and likely voter results has been about three points so far in Mr. Romney’s favor — about twice as large as the historical average.

As a technical matter, our forecast hedges against these polls somewhat. Not that many polling firms have reported these numbers so far, with most listing either registered voter or likely voter results but not both. And likely voter models can be a bit erratic when applied this early in the election cycle, when a lot of voters are not yet tuned in. It estimates that the gap will wind up being in the neighborhood of two-and-a-half points instead.

All this may seem like splitting hairs, but in a close election like this one, it can matter. A turnout gap is one of the bigger reasons for Democrats to be concerned about the election. It looks — for now at least — that Mr. Obama has enough support among the broader universe of American adults to win another term. But he could easily lose his office if those Americans who might be inclined to support him are not registered, or do not turn out to vote.

And yet, while this is good news for Mr. Romney, it does not qualify as great news for him. The reason is that, although a number of national polls are still reporting registered voter results, almost all the state polls released over the last month or two were conducted on a likely voter basis — his turnout advantage should already be priced into them. But Mr. Obama still leads more often than not when likely voter polls from battleground states have been released.

It’s all a bit of a mess, frankly. I suspect that part of the problem is that polling firms are applying likely voter methods that might have been designed 30 years ago to a modern polling universe of extremely low response rates (even the most thorough polling firms can only get about 10 percent of voters to return their calls), cellphone-only households, and an increasingly diverse and partisan electorate — and that is producing erratic and unpredictable results. There’s always some uncertainty about just who will turn out to vote, but there is more of it than usual this year.

Little Traction for Romney in Pennsylvania

One state where there seems to be less doubt about the outcome is Pennsylvania, where a Philadelphia Inquirer poll on Saturday was the latest to show Mr. Obama with a solid lead, putting him ahead 51 to 42 among likely voters. Mr. Obama has led in 21 consecutive polls of Pennsylvania and his margins seem to have widened a bit recently; the forecast model now gives him an 89 percent chance of winning it on Nov. 6.

Mr. Romney and affiliated groups have not been spending very much money in Pennsylvania, a decision that I have argued before was conceding the state too easily to Mr. Obama.

But at this point, Mr. Romney almost might as well follow through on that strategy. It will be harder for him to make up ground in Pennsylvania now — whereas Wisconsin opens up some additional Electoral College possibilities for Republicans, given how the polls have tightened there since Mr. Romney’s selection of Representative Paul D. Ryan as his running mate.

Pennsylvania has twice as many electoral votes as Wisconsin — but even accounting for that, it has fallen into eighth place on our list of tipping point states, whereas Wisconsin has risen to third.

A Pollster Finally Gets Missouri Right?

Rasmussen Reports had a flashy number for Mr. Obama in the Missouri poll it released on Friday — showing Mr. Obama ahead by a point there. But this was counterbalanced by a Mason-Dixon poll for the St. Louis Post-Dispatch, which had Mitt Romney up by seven points instead. Mr. Romney had led by nine points in their previous survey of Missouri.

The Mason-Dixon poll also had the Democratic incumbent, Claire McCaskill, pulling into a lead in the Senate race in Missouri, however. She now leads by nine points, a substantial swing from their July poll, when Representative Todd Akin led by five points, before his much-criticized remarks about rape.

I know it cuts somewhat against the FiveThirtyEight spirit to lump polls into binary categories of “right” and “wrong.” But the Mason-Dixon poll seems like a far more sensible take on the state of play in Missouri than the others we’ve seen since Mr. Akin’s remarks — showing a significant change in the Senate race there but a marginal impact at best on the presidential contest.

Romney’s Momentum Fades Slightly Heading Into Conventions

Over all, with a set of reas
onably favorable state polls on Thursday through Saturday after some poor ones earlier last week, Mr. Obama has rebounded a bit in our Electoral College forecast. The model now gives him a 69.3 percent chance of winning it, up from 66.7 percent on Wednesday. There’s also been a tiny shift back toward Mr. Obama in the national tracking polls, with Gallup now showing the race tied, and Rasmussen Reports putting Mr. Obama one point ahead as of Saturday.

It’s hard to tell whether there was a vice presidential ‘bounce’ for Mr. Romney that has since reversed itself — or whether this is all just a bunch of statistical noise. In this case, it may be something of a moot point, since the party conventions are likely to reset the momentum in one direction or another anyway.

Nate Silver is the founder and editor in chief of FiveThirtyEight.