Our regularly scheduled forecast update for Wednesday slipped through the cracks. The FiveThirtyEight forecast was not much changed based on Wednesday’s polls, however, with Barack Obama’s chances of winning the Electoral College increasing incrementally to 65.7 percent from 64.8 percent. 
 
 We’ll catch up with Thursday’s polls with the next update. In the meantime, I’m going to focus on one particular survey, the Gallup national tracking poll. 
 
 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. 
 
 Let me walk you through the rules for how the FiveThirtyEight model weighs the Gallup poll relative to all the other information it accounts for. This explanation will be modestly technical — you may want to skip ahead to the next section if you aren’t concerned with these details. 
 
 The Role of the Gallup Poll in the FiveThirtyEight Model 
 
 There are two major pieces of information that we’re looking to extract from each poll. One is simply the raw number — who is ahead or behind? The other is the trend it shows in the race — which candidate is gaining or losing ground? 
 
 Different types of polls are relatively more and relatively less useful for these purposes. Because national tracking polls like Gallup are published every day, they are useful for the trend part of the calculation, measuring the change in the race against a constant baseline. 
 
 Each poll receives a weight in the FiveThirtyEight trend-line calculation based on its sample size and its pollster rating. The model accounts for the fact that tracking polls use an overlapping set of interviews. A three-day tracking poll might consist of interviews conducted on Monday, Tuesday and Wednesday, for instance. When the polling firm issues its next release of the survey, a fresh set of interviews from Thursday will replace the ones from Monday in the sample. Thus, we reduce the weight assigned to each edition of a tracking poll to avoid counting the same interviews multiple times. 
 
 Even so, there are quite a few interviews conducted by a tracking poll over the course of a week — about 3,000 per week in the Gallup national tracking poll, for instance. 
 
 But Gallup is not the only national tracking poll. There are six published on most days; the others are from Rasmussen Reports, Ipsos, the RAND Corporation, Investors’ Business Daily and United Press International. (A seventh daily tracking poll, from Public Policy Polling, made its debut on Thursday.) 
 
 Of the daily tracking polls, the Gallup survey receives the largest weight in the trend-line calculation. It uses a larger sample size than most other polls, and it has a methodology that includes calls to cellphone voters. 
 
 On the other hand, the pollster ratings are also based in part on past accuracy, and Gallup’s performance is middling in that department. It mostly gets a lot of weight by comparison, since the tracking surveys are a mediocre group on the whole. 
 
 The trend-line adjustment also looks at other national polls when they are published, like the New York Times/CBS News or the Wall Street Journal/NBC News surveys. This is a high-quality group of polls; the disadvantage is that they are published only occasionally. 
 
 State polls are also useful for determining the overall trend in the race. In this case, the advantage is the abundance and diversity of data: there might be 10 or 20 state polls published on a typical day, often from 5 or 10 polling firms. 
 
 The trend-line calculation applies a 50 percent penalty to the weight assigned to state polls because trends in any one state could be an aberration. However, the states generally rise and fall together when there is a shift in the national climate — and if one candidate makes an especially large gain in one state, it must necessarily be counterbalanced by others in which it is below average. 
 
 The relative amount of weight assigned to each type of poll is fluid rather than fixed, and depends on the overall volume of data. On days when a large number of state polls is published but few national ones, they will generally be the more useful source for making inferences about the trend in the race. 
 
 But on average since Oct. 1, the Gallup national tracking poll has accounted for 12 percent of the information that the model uses to calculate the trend line. The other daily tracking polls, collectively, have accounted for 24 percent of the data, and the occasionally published national polls for 19 percent. Finally, the state polls account for about 45 percent of the data used to calculate the trend-line adjustment. 
 
 Photo 
 
 Thus, even though the Gallup national tracking poll is more influential than any other individual poll series in the FiveThirtyEight trend-line calculation, it still accounts for only about 12 percent of it. It can very easily be outweighed by the other polls if they are in disagreement with it. 
 
 As I mentioned, however, this is only half the battle. Once “old” polls are brought up to date by adjusting them to reflect the current trend in the race, we still need to take some kind of average of them. 
 
 The way the polls are employed to calculate the average is a little different than in calculating the trend line. Our research suggests, for instance, that state polls, rather than national polls, often provide a better estimate of the national popular vote, in addition to the Electoral College. 
 
 In addition, although the trend-line calculation relies fairly heavily on the quantity of polling — even a mediocre poll can be useful for measuring how the race is changing if it is published frequently — the polling average tends to place more emphasis on the quality of the poll. (Otherwise high-quality polls that are a bit of out-of-date can still have a fair amount of influence on the average. The problem with these polls being less recent is mitigated because the trend-line adjustment serves to make them more contemporary in the event that there has been a significant shift in the race.) 
 
 Over all, the Gallup daily tracking poll accounts for only about 3 percent of the weight 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. 
 
 Photo 
 
 This is, obviously, a rather detailed answer to the seemingly simple question of how much information is provided by the Gallup national tracking poll, as opposed to all the other state and national surveys. 
 
 Nevertheless, any rigorous attempt to consider the value of the Gallup poll would probably get you to something of the same answer. Perhaps the Gallup poll accounts for 5 or 10 percent of the information that an election analyst should evaluate on a given day. 
 
 The Gallup poll’s influence on the subjective perception about where the presidential race stands seems to be proportionately much greater than that, however — especially when the poll seems to diverge from the consensus. 
 
 This simply isn’t rational, in my view. As I discuss in my book, our first instincts are often quite poor when it comes to weighing information. We tend to put too much emphasis on the newest, most widely reported and most dramatic pieces of data — more than is usually warranted. 
 
 Gallup Performs Poorly When Out of Consensus 
 
 Usually, when a poll is an outlier relative to the consensus, its results turn out badly. 
 
 You do not need to look any further than Gallup’s track record over the past two election cycles to find a demonstration of this. 
 
 In 2008, the Gallup poll put Mr. Obama 11 points ahead of John McCain on the eve of that November’s election. 
 
 That was tied for Mr. Obama’s largest projected margin of victory among any of the 15 or so national polls that were released just in advance of the election. The average of polls put Mr. Obama up by about seven points. 
 
 The average did a good job; Mr. Obama won the popular vote by seven points. The Gallup poll had a four-point miss, however. 
 
 In 2010, Gallup put Republicans ahead by 15 points on the national Congressional ballot, higher than other polling firms, which put Republicans an average of eight or nine points ahead instead. 
 
 In fact, Republicans won the popular vote for the United States House by about seven percentage points — fairly close to the average of polls, but representing another big miss for Gallup. 
 
 Apart from Gallup’s final poll not having been especially accurate in recent years, it has often been a wild ride to get there. Their polls, for whatever reason, have often found implausibly large swings in the race. 
 
 In 2000, for example, Gallup had George W. Bush 16 points ahead among likely voters in polling it conducted in early August. By Sept. 20, about six weeks later, they had Al Gore up by 10 points instead: a 26-point swing toward Mr. Gore over the course of a month and a half. No other polling firm showed a swing remotely that large. 
 
 Then in October 2000, Gallup showed a 14-point swing toward Mr. Bush over the course of a few days, and had him ahead by 13 points on Oct. 27 — just 10 days before an election that ended in a virtual tie. 
 
 In 1996, Gallup had Bill Clinton’s margin over Bob Dole increasing to 25 points from nine points over the course of four days. 
 
 After the Republican convention in 2008, Gallup had John McCain leading Mr. Obama by as many as 10 points among likely voters. Although some other polls also had Mr. McCain pulling ahead in the race, no other polling firm ever gave him larger than a four-point lead. 
 
 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. ||||| Related Resources: 
 
 NOTE: The owner of this blog neither necessarily uses nor endorses the products advertised on this site. 
 
 
 
 blog advertising is good for you! ... 
 
 ***** ||||| 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. 
 
 What you think is going on in the race depends on whether you think the electorate will ultimately look more like Gallup's "likely voter" model, where the race is a blowout, or all registered voters, where it's a dead heat. So I asked Newport to explain the likely voter model to me. 
 
 "The likely voters model takes into account changes in the response to questions about how closely they're following and how enthusiastic they are," he said. "It's not just capturing underlying movement — it's representing changes in enthusiasm." 
 
 That sounds, I replied, like a model that would tend to overstate the effects of major events that favored one candidate or the other, as their supporters would grow temporarily more enthusiastic and attentive, while the other side would grow temporarily disillusioned. Newport agreed. "I wouldn't use the word 'overstate,' " he said. "But it would be very sensitive to changes in enthusiasm. The Denver debate clearly had an impact on Romney's people. I think your insight is correct there. Whether we see a dulling of that over the next several days is what I want to see."
– The latest Gallup poll suggests that Mitt Romney is still riding the wave from the first debate with a full 7-point lead nationally. Be skeptical, writes poll guru Nate Silver at the New York Times. Almost all other polls have the race roughly even or with Obama ahead. Silver offers a lengthy analysis, arguing that Gallup has a bad track record in similar instances over recent election cycles. Bottom line: "It's much more likely that Gallup is wrong and everyone else is right than the other way around." Ezra Klein at the Washington Post also sounds doubtful. He thinks Gallup's method of surveying likely voters, rather than registered voters, sounds like "a model that would tend to overstate the effects of major events that favored one candidate or the other, as their supporters would grow temporarily more enthusiastic and attentive, while the other side would grow temporarily disillusioned." Conservatives, though, are livid that Romney isn't getting credit for the poll and are going after Silver in particular given his status as a numbers whiz. "Anyone's who's pegging Obama at a 64.8 percent chance of winning the Electoral College at this point's obviously running a couple of quarts low already," writes Donald Douglas at the American Power blog.