In Florida, Tampa Is Essential to Romney Election Hopes

By MICAH COHEN

We continue our Presidential Geography series, a one-by-one examination of the peculiarities that drive the politics in all 50 states and the District of Columbia. Here, a look at Florida, the Sunshine State. FiveThirtyEight spoke with Lance deHaven-Smith, a professor of public administration and policy at Florida State University, and Daniel A. Smith, a professor in political science at the University of Florida.

The Republican Party has good reason to hold its national convention in Tampa, Fla. The Tampa area is the most competitive section of the most competitive region in one of the most competitive states in the nation - the perfect place to seek a glimmer of extra advantage in a closely-fought presidential contest.

In many ways, the Tampa area was the weakest link in the regional coalition that Barack Obama built to win Florida in 2008. The Tampa-St. Petersburg media market is home to a quarter of Florida's registe red Republicans, and Mr. Obama carried Hillsborough and Pinellas Counties - home to Tampa and St. Petersburg - by a smaller margin than Florida's other major population centers. If Mitt Romney wants to win the state, it represents the most attractive target.

And winning Florida is a must for Mr. Romney. Based on the simulations that the FiveThirtyEight forecast model ran on Tuesday, Mr. Romney has only a 0.3 percent chance of winning the election if he loses the state.

It is hard to conceive of Mr. Romney winning the election but losing Florida because Florida is an ever-so-slightly Republican-leaning state. If he loses it, he's probably having trouble elsewhere on the map as well. It's quite unlikely that Mr. Romney loses Florida but wins a state like Michigan or Pennsylvania, for instance.

Still, the state is idiosyncratic enough that it could behave differently, moving in one direction while the other swing states move in another. Each party begins with some strengths and weaknesses in the state, and regions that are vital to its path to victory there.

Just over a third of Florida's registered Democrats live in the Miami and West Palm Beach media markets, especially in Miami-Dade County, Broward County and Palm Beach County.

Broward County, in particular, is critical to Democratic margins in Florida. While Miami-Dade County is reliably Democratic, its large Cuban-American population leans Republican and keeps the county from tilting all the way to the left. Miami-Dade County is home to 58 percent of Florida's Hispanic Republicans and 34 percent of Hispanic Democrats. Without Broward County, however, Mr. Obama would have lost Florida in 2008; his statewide margin of victory (204,577 votes) was less than his margin in Broward (252,948 votes).

Democratic support has grown more recently in Orlando, a historically Republican city and the second main population center in the Interstate 4 corridor (along with Tam pa). Orlando's Orange County was just marginally Democratic in the 2000 and 2004 presidential elections. Then - partly because of an influx of non-Cuban Hispanics - Mr. Obama carried Orange County fairly easily in 2008, and the county itself is probably out of reach for Republicans now.

“It's really tipping the state,” Mr. deHaven-Smith said. A potential dream scenario for Democrats - and a nightmare for Republicans - is if the demographic shifts in this region are enough to shift Florida from being slightly Republican-leaning to strictly neutral, or slightly Democratic-leaning instead.

The Jacksonville area has also moved to the left, although from a more conservative starting point and for slightly different reasons. That region, which has a significant military presence, is known for its culturally moderate, business-oriented Republicans, Mr. Smith said. Former President George W. Bush won Jacksonville's Duval County with 58 percent of the vote in both 200 0 and 2004.

Those same voters are still a majority, but just barely. Duval County has become more competitive as its African-American population has grown and as black turnout has increased, Mr. deHaven-Smith said. In 2008, Mr. Obama lost Duval by just one percentage point.

East of Jacksonville, Florida begins to look and feel like its northern neighbors, Georgia and Alabama. Affectionately known as the “Redneck Riviera“, the Florida Panhandle's beautiful beaches are dotted by resorts and military installations. The area is culturally conservative and heavily Republican, but most of the counties in the Panhandle are sparsely populated.

The last predominately Republican area of the state is southwest Florida, where a string of retirement communities stretch along the coast, giving the G.O.P. a solid base of reliable voters. More affluent retirees tend to live in Collier County, while more working-class retirees have settled in Charlotte County, Mr. deHav en-Smith said. But both communities, like Fort Myers's Lee County and most of the rest of Florida, were hit hard by the collapse of the housing sector.

The Bellwether

That leaves the Tampa area as neutral - but critical - turf. Of course, both Democrats and Republicans can do a little worse in one region if they do a little better in another. But in general, carrying Tampa has been the final step for statewide winners. In every election since 1960 the presidential candidate who carried Florida has also carried Tampa's Hillsborough County.

Economically and ethnically, Hillsborough County is a fairly good microcosm of America. The county's Democratic core in Tampa is balanced by the city's Republican suburbs, and recent Hispanic growth has been accompanied by exurban growth, maintaining the county's partisan equilibrium.

The Bottom Line

Florida is the closest state according to the FiveThirtyEight forecast; Mr. Obama was a nominal 52 percent favor ite there as of Tuesday, but it has flipped back and forth between the candidates many times.

Still, and particularly so long as Mr. Obama seems to hold a clearer advantage in other swing states like Ohio, it is much easier to conceive of Mr. Obama winning the election without Florida than Mr. Romney. For that reason, it represents more of an offensive state for him.

For over a year, Mr. Obama has been building an extensive infrastructure in the state, despite the state's reputation for being dominated by the advertising “air war.” The Obama campaign has opened 73 field offices in Florida compared with the Romney campaign's 28.

In Mr. Romney's favor is Florida's still struggling economy. In particular, the state's housing sector continues to flounder. Apart from the general distaste that a poor economy can cultivate for an incumbent, the Obama campaign's efforts to reach out to voters have been complicated by Florida's many home foreclosures, which have uprooted thousands and rendered voter lists inaccurate.

Ultimately, the calculus for undecided Tampa voters is the same for Florida voters, which is much the same as it is for undecided voters elsewhere: how much is the president to blame for the tepid economic recovery, in Florida and the nation? And is Mr. Romney a suitable alternative? The way voters in Tampa answer those questions could help determine the next president.

Aug. 28: A Moment of Polling Clarity

August 28, 2012, 11:44 pm

By NATE SILVER

At FiveThirtyEight, we're usually consumed by how much the polls disagree with one another, and where the race stands once you filter through all that noise. But every now and then, the pollsters make our job easy.

Over the past several days, there have been 15 national polls released. It looks like everybody has been trying to get numbers out as a baseline before the party conventions. And they tell a pretty consistent story.

Nine of the 15 polls have President Obama ahead by either one or two percentage points. Three have Mr. Obama ahead by a slightly larger margin, between four and six percentage points. Another three have Mr. Romney ahead, each by a single percentage point.

On average betwee n the 15 surveys, Mr. Obama leads by 1.6 percentage points. While there are some modest differences between them, pretty much every poll is within the margin of error of the others.

Enjoy this moment of relative consensus in the polls; it probably won't last long.

Swing State Connecticut?

To get a more controversial polling result, we instead have to turn toward Connecticut, where Quinnipiac released a poll on Tuesday showing a relatively close race. Quinnipiac had Mr. Obama by seven points in Connecticut, making this the third consecutive poll to show Mr. Romney within single digits there.

Our forecast model's view is that these surveys slightly underrate Mr. Obama's position in Connecticut; it projects that he'll eventually win the state by 10 or 11 percentage points. Still, that would be a big drop-off from 2008, when he won the state by 22 points.

It's not that hard to see how Mr. Romney could be overperforming i n Connecticut. It has lots of wealthy voters who are employed in finance, particularly at private equity firms and hedge funds, industries that have become skeptical of Mr. Obama's performance. Mr. Romney has raised more money than Mr. Obama in Connecticut, about $5.2 million in itemized contributions, against $3.5 million for the president.

Could Connecticut actually figure into the electoral math? It's obviously not likely. The model gives Connecticut just a 0.2 percent chance (about 1 chance in 500) of being the tipping point state and casting the decisive votes in the Electoral College.

Still, it's interesting to contemplate cases in which Republicans began to be more competitive again in the Northeast. In this hypothetical map, for example, the Republican candidate wins Connecticut, New Jersey and New Hampshire, enough to give him a winning map with 272 electoral votes, despite his losing most of the swing states in the West and the Midwest.

The odds a re hundreds-to-one against a map like this coming to fruition this year. But it could be more plausible in 2016 if the Republicans nominated a relatively moderate candidate who downplayed social issues - positions that have turned off a lot of voters in states like Connecticut and New Jersey who might vote G.O.P. if they were going by their pocketbooks.

In the meantime, a relatively strong performance by Mr. Romney in Connecticut could help the Republican Senate candidate, Linda E. McMahon, to carry the state. She held a lead over her Democratic opponent, Representative Christopher S. Murphy, in the Quinnipiac poll.

Ms. McMahon did not wear well with voters over the course of the 2010 campaign, and she is fighting against a lot of partisan gravity in Connecticut, which hasn't elected a Republican to the Senate since Prescott Bush in 1956. But if Mr. Romney can keep the race within single digits, she'll have a considerably better chance of holding on.

Aug. 27: Michigan Isn\'t a Tossup

By NATE SILVER

In this update, I'm going to focus on the polling we've seen in one particular state, Michigan, where there is an exceptionally wide spread between firms showing relatively strong numbers for Barack Obama, and those which have good numbers for Mitt Romney instead.

But first let me mention a poll that is a bit easier to interpret. The Washington Post and ABC News released their latest national poll on Monday, and it had favorable numbers for Mr. Romney, showing him one point ahead of Barack Obama among registered voters.

Past Washington Post/ABC News polls have often shown a pretty tight race, so this poll doesn't necessarily speak to a dramatic change in the state of play. But sometimes a more basic point gets lost when we get as detail-oriented about the polls as we sometimes do at FiveThirtyEight.

The Post/ABC poll is a very good survey, with strong methodology and a strong track record. The point is simply that it's good for a candidate when a strong polling firm shows him doing well. In any election, there are going to be polling firms that publish relatively stronger and relatively weaker numbers for a candidate; this is one of those surveys that you'd very much like to have on your side. And so far this cycle, Mr. Romney has tended to get the better results from the Post/ABC poll.

The Mysterious Polling in Michigan

There are also surveys that you don't necessarily want on your side, however, and some states seem to have a concentration of them. One of them is Michigan, where since mid-July we've seen polls showing everything from a 14-point lead for Mr. Obama in Michigan to a 4-point lead for Mr. Romney. That is a remarkably wide spread - too wide to be caused by statistical variance alone. Someone is getting this race wrong.

Our forecast model tends to side with the polls showing Mr. Obama in a reasonably good position in Michigan. It's extremely doubtful that he's ahead by double-digits there - and almost certainly not by 14 points - but the forecast projects a six- or seven-point victory for Mr. Obama in Michigan on Nov. 6. Let me explain how it comes to that conclusion.

In the table below, I've broken down the Michigan polls into two categories: those conducted by firms that frequently survey states outside of Michigan, and those that poll Michigan only, or Michigan and one other state.

The national polling firms, like Rasmussen Reports, Public Policy Polling, and Marist College, show Mr. Obama ahead by an average of seven points in Michigan. By contrast, the Michigan-only pollsters show him ahead by only two points.

The advantage of the national pollsters is that we have a good sense for how to interpret their results. Some are Democratic-leaning and some are Republican-leaning - but whatever “house effect” they tend to show, it is usually fairly consistent from state to state.

By contrast, when a polling firm takes surveys in one state only, and its results diverge substantially from the consensus, it's harder to tell what is going on. It could be that there is something about Michigan in particular they are seeing. Or it could be something more intrinsic to the methodology: that if the firm shows good numbers for Mr. Romney in Michigan, for example, it would also do so in Colorado, or Virginia, or Ohio, if only they surveyed those states.

The model is designed to mostly prefer the latter interpretation. If a local polling firm diverges substantially from the consensus, it infers that the results show a strong “house effect,” rather than providing any particular insight about the state. It doesn't entirely dismiss the poll, but it treats it skeptically.

But isn't local knowledge a good thing? It can be, and there are some outstanding state polls conducted by local newspapers or local universities, which are rewarded accordingly in our pollster ratings . However, there are also some very questionable ones.

In Michigan, there are two local polling firms in particular that have shown poor numbers for Mr. Obama. One is Mitchell Research, which just published a poll showing a tie there. The other is Foster McCollum White Baydoun, which had Mr. Romney ahead by four points in its last survey.

Foster McCollum White Baydoun actually does survey one state apart from Michigan: it released a poll of Florida last week. In that survey, it showed Mr. Romney ahead by almost 15 points - perhaps the biggest outlier we've seen in any individual poll so far this year.

As I mentioned when that Florida poll came out, this firm anticipates a big decline in participation among groups like younger voters that are ordinarily inclined to support Democratic candidates. The initial news release of the Florida poll appeared to show that the firm anticipated that just 11 percent of Florida voters would be under age 50 - in contrast to about half the Florida electorate in 2008, according to exit polls. A principal of the firm, Eric Foster, later wrote me to say that the news release had been incomplete, and voters under the age of 50 had actually been weighted to make up 27 percent of the poll instead.

That's still an implausibly large drop-off, in my view, from 2008. It may be because the Foster McCollum White Baydoun likely-voter model looks for voters who, as they described it, participated in “odd year municipal and county elections” - where turnout is tiny as compared with what it will be on Nov. 6. In any event, this method seems likely to produce extremely Republican-leaning results - whether applied to Michigan, to Florida or to any other state.

At least Foster McCollum White Baydoun have a methodology of some kind, even if it isn't one that I would recommend. What Mitchell Research is doing in Michigan is a little more troubling.

The head of Mitchell Research, Steve Mitchell , wrote a long memo accompanying his poll release on Monday. In that poll, he weighted the survey to assume that African-Americans would make up only 8 percent of Michigan's turnout. By contrast, black voters represented 12 percent of the turnout in Michigan in 2008 according to exit polls, and 14 percent according to another source, the Current Population Survey. Blacks also made up 13 percent of Michigan's vote in 2004 and 11 percent in 2000, according to exit polls. African-American participation is sometimes lower in midterm election years, but blacks were 12 percent of Michigan's electorate in 2006, the exit poll reported that year. (There was no exit polling in Michigan in 2010.)

So why only 8 percent this year? Mr. Mitchell wrote that he simply doesn't believe the exit polls:

“African-American participation in this poll is 8%, not 12%, which is the percentage of the population but not likely voters. I do not believe blacks represented 12% of the vote in 2008 and I don't believe they will in 2012. Having polled this state for 26 years, blacks have represented about 7%-8% of all votes cast in every statewide race. At best, it went to 9% four years ago. It will not reach that level this year.”

What is the evidence for Mr. Mitchell's claim? He didn't present any of it in the memo. The exit polls certainly aren't perfect, but they've been consistent from year to year and also seem to agree with Census Bureau data. (Another fact that Mr. Mitchell cites - that African-Americans represent 12 percent of the overall population in Michigan - is also slightly incorrect; they made up 14 percent of Michigan's population as of 2011, according to the Census Bureau.)

Perhaps Mr. Mitchell means that only about 8 percent of respondents are black when he takes his surveys. But response rates to political surveys have been much lower among African-Americans for many years. The problems may be worse in a su rvey, like Mr. Mitchell's, that does not call cellphone voters, since African-Americans are more likely to rely on cellphones in lieu of landline phones.

It is precisely because of this problem that essentially all polling firms do weight by race, usually calibrating their numbers based on Census Bureau or exit poll data. Mr. Mitchell, however, seems to have his own ideas about what Michigan's electorate will look like. There is a certain amount of art in political polling, but I've never heard of a pollster treating the demographic makeup of a state as essentially a matter of opinion.

Mr. Mitchell's demographic weights account for much of the difference between his polls and those of the other firms that are active in Michigan; a decrease in the African-American vote from 12 percent to 8 percent would harm Mr. Obama's numbers by a net of about four percentage points there. If you have some reason to discount the Mitchell Research and Foster McCollum White Baydou n polls, it is much harder to make the case that the presidential and Senate races in Michigan are a “tossup,” as some other Web sites have characterized it.

To be clear, our forecast model doesn't “know” all of this detail about the Mitchell Research and Foster McCollum White Baydoun polls. It discounts the results from these firms simply because that's what it's programmed to do whenever it encounters a local polling firm whose results diverge substantially from the consensus; this method works to Mr. Obama's benefit in some states, and Mr. Romney's in others.

But my personal view is that the model is making the right inference in the case of Michigan, and that the methodological choices that these polls have made are hard to defend. Perhaps 90 or 95 percent of the time, taking a simple average of the polls will work just about as well as the more complicated FiveThirtyEight method. But this is rare instance where taking all the polls at face value may be a mistake, and the additional checks-and-balances the FiveThirtyEight method applies are worth the trouble.

Aug. 27: Michigan Isn\'t a Tossup

By NATE SILVER

In this update, I'm going to focus on the polling we've seen in one particular state, Michigan, where there is an exceptionally wide spread between firms showing relatively strong numbers for Barack Obama, and those which have good numbers for Mitt Romney instead.

But first let me mention a poll that is a bit easier to interpret. The Washington Post and ABC News released their latest national poll on Monday, and it had favorable numbers for Mr. Romney, showing him one point ahead of Barack Obama among registered voters.

Past Washington Post/ABC News polls have often shown a pretty tight race, so this poll doesn't necessarily speak to a dramatic change in the state of play. But sometimes a more basic point gets lost when we get as detail-oriented about the polls as we sometimes do at FiveThirtyEight.

The Post/ABC poll is a very good survey, with strong methodology and a strong track record. The point is simply that it's good for a candidate when a strong polling firm shows him doing well. In any election, there are going to be polling firms that publish relatively stronger and relatively weaker numbers for a candidate; this is one of those surveys that you'd very much like to have on your side. And so far this cycle, Mr. Romney has tended to get the better results from the Post/ABC poll.

The Mysterious Polling in Michigan

There are also surveys that you don't necessarily want on your side, however, and some states seem to have a concentration of them. One of them is Michigan, where since mid-July we've seen polls showing everything from a 14-point lead for Mr. Obama in Michigan to a 4-point lead for Mr. Romney. That is a remarkably wide spread - too wide to be caused by statistical variance alone. Someone is getting this race wrong.

Our forecast model tends to side with the polls showing Mr. Obama in a reasonably good position in Michigan. It's extremely doubtful that he's ahead by double-digits there - and almost certainly not by 14 points - but the forecast projects a six- or seven-point victory for Mr. Obama in Michigan on Nov. 6. Let me explain how it comes to that conclusion.

In the table below, I've broken down the Michigan polls into two categories: those conducted by firms that frequently survey states outside of Michigan, and those that poll Michigan only, or Michigan and one other state.

The national polling firms, like Rasmussen Reports, Public Policy Polling, and Marist College, show Mr. Obama ahead by an average of seven points in Michigan. By contrast, the Michigan-only pollsters show him ahead by only two points.

The advantage of the national pollsters is that we have a good sense for how to interpret their results. Some are Democratic-leaning and some are Republican-leaning - but whatever “house effect” they tend to show, it is usually fairly consistent from state to state.

By contrast, when a polling firm takes surveys in one state only, and its results diverge substantially from the consensus, it's harder to tell what is going on. It could be that there is something about Michigan in particular they are seeing. Or it could be something more intrinsic to the methodology: that if the firm shows good numbers for Mr. Romney in Michigan, for example, it would also do so in Colorado, or Virginia, or Ohio, if only they surveyed those states.

The model is designed to mostly prefer the latter interpretation. If a local polling firm diverges substantially from the consensus, it infers that the results show a strong “house effect,” rather than providing any particular insight about the state. It doesn't entirely dismiss the poll, but it treats it skeptically.

But isn't local knowledge a good thing? It can be, and there are some outstanding state polls conducted by local newspapers or local universities, which are rewarded accordingly in our pollster ratings . However, there are also some very questionable ones.

In Michigan, there are two local polling firms in particular that have shown poor numbers for Mr. Obama. One is Mitchell Research, which just published a poll showing a tie there. The other is Foster McCollum White Baydoun, which had Mr. Romney ahead by four points in its last survey.

Foster McCollum White Baydoun actually does survey one state apart from Michigan: it released a poll of Florida last week. In that survey, it showed Mr. Romney ahead by almost 15 points - perhaps the biggest outlier we've seen in any individual poll so far this year.

As I mentioned when that Florida poll came out, this firm anticipates a big decline in participation among groups like younger voters that are ordinarily inclined to support Democratic candidates. The initial news release of the Florida poll appeared to show that the firm anticipated that just 11 percent of Florida voters would be under age 50 - in contrast to about half the Florida electorate in 2008, according to exit polls. A principal of the firm, Eric Foster, later wrote me to say that the news release had been incomplete, and voters under the age of 50 had actually been weighted to make up 27 percent of the poll instead.

That's still an implausibly large drop-off, in my view, from 2008. It may be because the Foster McCollum White Baydoun likely-voter model looks for voters who, as they described it, participated in “odd year municipal and county elections” - where turnout is tiny as compared with what it will be on Nov. 6. In any event, this method seems likely to produce extremely Republican-leaning results - whether applied to Michigan, to Florida or to any other state.

At least Foster McCollum White Baydoun have a methodology of some kind, even if it isn't one that I would recommend. What Mitchell Research is doing in Michigan is a little more troubling.

The head of Mitchell Research, Steve Mitchell , wrote a long memo accompanying his poll release on Monday. In that poll, he weighted the survey to assume that African-Americans would make up only 8 percent of Michigan's turnout. By contrast, black voters represented 12 percent of the turnout in Michigan in 2008 according to exit polls, and 14 percent according to another source, the Current Population Survey. Blacks also made up 13 percent of Michigan's vote in 2004 and 11 percent in 2000, according to exit polls. African-American participation is sometimes lower in midterm election years, but blacks were 12 percent of Michigan's electorate in 2006, the exit poll reported that year. (There was no exit polling in Michigan in 2010.)

So why only 8 percent this year? Mr. Mitchell wrote that he simply doesn't believe the exit polls:

“African-American participation in this poll is 8%, not 12%, which is the percentage of the population but not likely voters. I do not believe blacks represented 12% of the vote in 2008 and I don't believe they will in 2012. Having polled this state for 26 years, blacks have represented about 7%-8% of all votes cast in every statewide race. At best, it went to 9% four years ago. It will not reach that level this year.”

What is the evidence for Mr. Mitchell's claim? He didn't present any of it in the memo. The exit polls certainly aren't perfect, but they've been consistent from year to year and also seem to agree with Census Bureau data. (Another fact that Mr. Mitchell cites - that African-Americans represent 12 percent of the overall population in Michigan - is also slightly incorrect; they made up 14 percent of Michigan's population as of 2011, according to the Census Bureau.)

Perhaps Mr. Mitchell means that only about 8 percent of respondents are black when he takes his surveys. But response rates to political surveys have been much lower among African-Americans for many years. The problems may be worse in a su rvey, like Mr. Mitchell's, that does not call cellphone voters, since African-Americans are more likely to rely on cellphones in lieu of landline phones.

It is precisely because of this problem that essentially all polling firms do weight by race, usually calibrating their numbers based on Census Bureau or exit poll data. Mr. Mitchell, however, seems to have his own ideas about what Michigan's electorate will look like. There is a certain amount of art in political polling, but I've never heard of a pollster treating the demographic makeup of a state as essentially a matter of opinion.

Mr. Mitchell's demographic weights account for much of the difference between his polls and those of the other firms that are active in Michigan; a decrease in the African-American vote from 12 percent to 8 percent would harm Mr. Obama's numbers by a net of about four percentage points there. If you have some reason to discount the Mitchell Research and Foster McCollum White Baydou n polls, it is much harder to make the case that the presidential and Senate races in Michigan are a “tossup,” as some other Web sites have characterized it.

To be clear, our forecast model doesn't “know” all of this detail about the Mitchell Research and Foster McCollum White Baydoun polls. It discounts the results from these firms simply because that's what it's programmed to do whenever it encounters a local polling firm whose results diverge substantially from the consensus; this method works to Mr. Obama's benefit in some states, and Mr. Romney's in others.

But my personal view is that the model is making the right inference in the case of Michigan, and that the methodological choices that these polls have made are hard to defend. Perhaps 90 or 95 percent of the time, taking a simple average of the polls will work just about as well as the more complicated FiveThirtyEight method. But this is rare instance where taking all the polls at face value may be a mistake, and the additional checks-and-balances the FiveThirtyEight method applies are worth the trouble.

Aug. 26: Little Momentum in Polls in Advance of Conventions

By NATE SILVER

The FiveThirtyEight forecast for Sunday gives Barack Obama a 69.4 percent chance of winning the Electoral College on Nov. 6. That's essentially unchanged from Saturday - although there have been some modest shifts back and forth in the numbers over the course of the past two weeks since Mitt Romney named Representative Paul D. Ryan of Wisconsin as his vice-presidential nominee.

Mr. Romney was given a 28.0 percent chance of winning the Electoral College on Aug. 10, the day before he officially announced Mr. Ryan as his pick. The forecast then moved somewhat toward Mr. Romney after a series of improved polling in swing states for the newly minted Republican ticket, achieving a peak of 33.3 percent on Wednesday. It has since receded slightly to 30.6 percent, however, as Mr. Obama held leads in a number of swing state polls late last week.

These shifts could be consistent with a small vice-presidential “bounce” for Mr. R omney which has since faded - perhaps as less favorable stories for Republicans, like the comments on abortion and rape made by Representative Todd Akin of Missouri, have come to dominate the news cycle.

But these are only very minor differences - the model estimates that Mr. Romney gained a net of perhaps one percentage point in the popular vote after his selection of Mr. Ryan, and has lost perhaps half a percentage point since then. Changes of that magnitude could potentially be caused by statistical noise, as well as by real shifts of opinion.

What's clearer is that Mr. Romney did not get as large a bounce in the polls from his vice-presidential pick as most past candidates have - a fact that can arguably be read as a bearish sign for him.

The Republicans do seem to have made some headway in Mr. Ryan's native state of Wisconsin, however. And their last few polls in Florida have been been reasonably strong, defying the conventional wisdom that suggested M r. Ryan's views on entitlement programs could be damaging among the senior population in that state.

Can Romney Achieve Focus in Tampa?

Political coverage over most of the past two months has veered between hard news events like the Supreme Court's ruling on Mr. Obama's health care bill, and a set of personal issues that can occupy the news cycle for days at a time, like Mr. Romney's tax returns or the comments made by Mr. Akin.

Both campaigns also seem to have been in trench-warfare mentality, with a focus on day-to-day tactics rather than long-term strategy.

The Republican convention in Tampa could represent an opportunity for Mr. Romney to break through the noise and show some more sustained improvement in his polling. Conventions almost always do produce bounces in the polls. These bounces fade, but an especially large or an especially small bounce can be an indicator of how the rest of the race is likely to proceed.

However, the Republicans face an unusual pair of challenges at their convention: first, that the interval separating the Republican convention from the Democratic one in Charlotte is extremely short; and second, that the news media's attention could be divided between the developments in Tampa and those in the Gulf of Mexico, where Hurricane Isaac is a threat to New Orleans and other cities on the Gulf Coast.

Sunday's Polls

The only new state poll out on Sunday was in Ohio, where the Columbus Dispatch published a poll showing Mr. Obama and Mr. Romney tied at 45 percent each.

The Columbus Dispatch poll is unusual: It is conducted entirely by mail, with surveys sent out to a random selection of Ohio voters.

The potential problem with this polling method is that because returning a mail survey requires more effort than taking a phone call, the response rates are likely to be lower and could potentially overrate the strength of the candidate with the more enthusiastic supporters .

However, it might be noted that all forms of survey research - certainly including telephone polling - face a problem of low response rates. And historically, the performance of the Columbus Dispatch poll has been about average, with some strong years and some poor ones.

If its survey differed greatly from the consensus, I would be a little wary of it - but showing a tie in Ohio is not that different from the average of surveys there, which puts Mr. Obama ahead but by a narrow margin. In short, I don't have any problem including Dispatch's survey alongside the rest of the Ohio polls. Mr. Romney's chances of winning Ohio improved slightly in our forecast as a result of the poll, increasing to 33 percent from 31 percent on Saturday.

Mr. Romney got slightly unfavorable results in the national polls that were out on Sunday, however, with the Rasmussen Reports tracking poll showing Mr. Obama pulling into a 2-point lead among likely voters - a better result tha n it appears for Mr. Obama since Rasmussen's polls have been somewhat Republican-leaning this cycle.

There was also a poll of likely voters from the Tarrance Group, a well-respected Republican polling firm, which gave Mr. Obama a 1-point lead among likely voters.

How Will Party Conventions Affect the Presidential Race?

By JOHN SIDES

The Republican and Democratic national conventions bring the possibility of change to this static presidential race.  But how will it change, and how much?  Here is some of what we know.

The party conventions typically cause the largest swings in the polls during the presidential campaign.  During the convention season, the polls are unstable and likely to change more than at any point afterward, according to research by the political scientists Robert Erikson and Christopher Wlezien.

As is well-known, a party convention typically creates a “bump” or “bounce” for the candidate being nominated. Across presidential elections from 1964 to 2008, this has typically meant a 5-6 point increase, according to both political science research and the tabulations of pollsters like Gallup.

This leads to a first question: Why a bounce at all?  Why would the conventions have this effect in the first place?  After all, they are largely symbolic events, lacking in real drama and thus covered less and less by news organizations and watched by fewer and fewer viewers.  (This paper by political scientist Costas Panagopolous documents the decline.)

One reason is that conventions generate a larger “dose” of information than is provided by the daily ebb and flow of news coverage.  Thomas Holbrook's study of campaigns from 1984-92 found that front-page coverage of each presidential candidate rose sharply during his party's convention.

A second reason is that the news coverage during the convention favors the candidate being nominated. There are typically no increases in the coverage of the Republican candidate during the Democratic National Convention, and vice versa. Thus, unlike the later debates, a convention allows the candidate to present himself, Mr. Holbrook writes, “in a relatively uncontested format.”  So conventions typically generate not just news, but favorable news for the candidates.

Next question: How big is the bounce?  The bounces have ranged from essentially zero (John Kerry in 2004) to about 14 points (Barry Goldwater in 1964 and Bill Clinton in 1992).  Two things appear to affect the size of the bounce, according to Mr. Holbrook in a recent blog post.  One is how well the candidate is doing, relative to expectations. Here, we can think about expectations in terms of the underlying political and economic fundamentals.  So a candidate running behind what the economy and other fundamentals would predict should get a larger convention bounce.  A second factor is the timing of the conventions.  Traditionally, the party whose convention occurs first - the party currently not in control of the White House - has had the larger bounce, which makes sense if the challenger is not as well-known as the incumbent and therefore voters have not formed as strong an opinion about the challenger.  However, holding the conventions close together and somewhat later in the campaign season, as in 2008 and 2012, seems to mute the advantage of going first.

Final question: Will the bounce persist? Will the changes during this period have lasting benefits for President Obama or Mitt Romney?  The term “bounce” makes it seem as if the candidates numbers will go up and then down, rendering any impact temporary.  In fact, the conventions tend to leave a more permanent imprint.  Mr. Erikson and Mr. Wlezien in their study of the 1952-2008 presidential elections find:

On average, the party that gains from before to after the conventions maintains its gains in the final week's polls…Although the convention season is the time for multiple bounces in the polls, one party ends up with an advantage when the dust clears.

Of course, this is an average result, not a description of every election.  In 2008, Mr. Obama was behind in several polls after the Republican conve ntion, only to cruise to a comfortable victory.

What does this mean for 2012?  I'll leave the exact forecast to Nate, but I would expect only small bumps for either party.  Neither candidate is really polling above or below expectations at the moment.  The fundamentals going into the race suggest an Obama victory, but by a relatively small margin - and that's exactly where the polls are right now.  Moreover, scheduling the convention late in the summer and back-to-back should mitigate their impact.  And there is only a small number of self-described undecided voters, which may help explain why another high-profile event, the naming of Representative Paul D. Ryan as the running mate, has not really moved the national polls.

To be sure, even “small bumps” might be enough to put the race on its head, moving Mr. Romney from a slight underdog to a slight front-runner.  If that proves true, the question is whether Mr. Romney will sustain that lead through Ele ction Day.

Aug. 25: An Above-Average \'Likely Voter Gap\' for Romney

By NATE SILVER

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 po lls 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 numb er 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

< p>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 categ ories 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 reasonably 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.