Why the Big Difference in Polls?

Fern

Elite Member
Sep 30, 2003
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Note: it's a long post, please don't quote the whole thing if responding

This seems a fairly good article on the adjustments pollsters make to the (raw) results of their polling. As explained in the article, not only do they adjust for *factual* items such as those found in US Census data, but they make *guesses* about new trends, if any, this year may be different than past years (e.g., female and black voter turn-out).

Are the polls accurate? Well, that's anybody's guess; since they differ so much one-from-the-other obviously some are wrong.

I hear some say McCain will do better because many female Dems will not be voting for Obama. They've (women) claimed they tell polsters "Yeah, I'm a Dem I'll and will be voting for Obama" when they are planning not to. I've never heard one say it's because of Palin, but rather the lingering dis-like over HRC's alleged mistreatment by the Obama camaign. I don't think anybody really knows if there are significant numbers of these people. Personally, I think not, but IDK. (this would be a case of people not being honest with polsters as mentioned below)

Others say the race and/or inexperience issue(s) may cause significant numbers of voters to change their minds (or really only make it up) at the polls. We do know that there are a significant number who only decide once at the booth. Often, which way they go decides the race. (As mentioned below, polls with very low number of undecided voters may be less accurate than other because the polsters pushed people into a decision on the phone. (Who knows if they'll stick with it, or change their minds?)

This year turn-out is big deal IMO. That's Karl Rove's speciality and the over-arching theme of his *masterplans* in campaigns (Dick Morris's uses a different strategy). Changing events, bad/good weather and all sorts of other factors can affect turnout and ruin a polling company's predictions making their poll results inaccurate. This year's big *turnot* question may be that of college aged voters. Boom or bust?

Link

WASHINGTON ? Barack Obama is galloping away with the presidential race. Or maybe he has a modest lead. Or maybe he and John McCain are neck and neck.

Confusing? Sure, thanks to the dueling results of recent major polls.

In the past week, most surveys have shown Democrat Obama with a significant national lead over Republican McCain. Focusing on "likely voters" ? as many polling organizations prefer this close to Election Day ? an ABC News-Washington Post survey showed Obama leading by 11 percentage points. A Wall Street Journal-NBC News poll had the same margin, while the nonpartisan Pew Research Center gave Obama a 14-point edge.

But others had the race much closer. CNN-Opinion Research detected an Obama lead of 5 points. The George Washington University Battleground Poll had Obama up by 4 points. And an Associated Press-GfK poll showed Obama at 44 percent and McCain at 43 percent ? in effect, a tie.

How can this be? Some questions and answers about why the polls differ.

Q: Don't pollsters simply ask questions, tally the answers and report them?

A: No. After finishing their interviews ? usually with about 1,000 people, sometimes more ? they adjust the answers to make sure they reflect Census Bureau data on the population like gender, age, education and race. For example, if the proportion of women interviewed is smaller than their actual share of the country's population, their answers are given more "weight" to balance that out. But some pollsters make these adjustments differently than others. And while most polling organizations including the AP do not modify the responses to reflect some recent tally of how many Democrats, Republicans and independents there are, some do.

Q: Are those the only changes made?

A: No. As Election Day nears, polling organizations like to narrow their samples to people who say they are registered voters. They often narrow them further to those they consider likely voters. That's because in a country where barely more than half of eligible voters usually show up for presidential elections, pollsters want their polls to reflect the views of those likeliest to vote.

Q: Is that hard to do?

A: Quite hard, since no one will truly know who will vote on Election Day until that day is over. In fact, virtually every polling organization has its own way of determining who likely voters are.

Like many polling organizations, the AP asks several questions about how often people have voted in the past and how likely they are to vote this year, and those who score highest are considered likely voters.

Q: Why is this such a problem?

A: Because nobody is 100 percent sure how to do this properly. And the challenge is being compounded this year because many think Obama's candidacy could spark higher turnout than usual from certain voters, including young voters and minorities. The question pollsters face is whether, and how, to adjust their tests for likely voters to reflect this.

In identifying likely voters, the AP does not build in an assumption of higher turnout by blacks or young voters. Pew Director Andrew Kohut says that reflecting exceptionally heavy African-American turnout in the Democratic primaries, Pew's model of likely voters now shows blacks as 12 percent of voters, compared to 9 percent in 2004.

Underscoring the uncertainty, the Gallup Poll is using two versions of likely voters this year ? a traditional one that asks about peoples' past voting behavior and their current voting intentions; and an expanded one that only looks at how intent they are on voting this year, which would tend to include more new voters.

Q: What else might cause differences?

A: The groups pollsters randomly choose to interview are bound to differ from each other, and sometimes do significantly.

Every poll has a margin of sampling error, usually around 3 percentage points for 1,000 people. That means the results of a poll of 1,000 people should fall within 3 points of the results you would expect had the pollster instead interviewed the entire population of the U.S. But ? and this is important ? the results are expected to be that accurate only 95 percent of the time. That means that one time in 20, pollsters expect to interview a group whose views are not that close to the overall population's views.

Q: Are the differences among polls this year that unusual?

A: Not wildly, but that doesn't make them less noticeable. There's a big difference between a race that's tied in the AP poll, and Pew's 14-point Obama lead. But because of each poll's margin of error, those differences may be a bit less ? or more ? than meet the eye.

That's because each poll's margin of sampling error should really be applied to the support for each candidate, not the gap between them.

Take the AP poll, which has a margin of error of plus or minus 3.5 percentage points. Obama's 44 percent support is likely between 48 percent and 40 percent. McCain's 43 percent is probably between 47 percent and 39 percent.

When support for candidates is measured in ranges like that, some polls' findings could overlap ? or grow worse.

Q: Are people always willing to tell pollsters who they're supporting for president?

A: No, and that's another possible source of discrepancies. Some polling organizations gently prod people who initially say they're undecided for a presidential preference, others do it more vigorously. The AP's poll, for example, found 9 percent of likely voters were undecided, while the ABC-Post survey had 2 percent.
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Fern
 

Dr. Zaus

Lifer
Oct 16, 2008
11,770
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Auspice bias (different people will answer a poll by the new york times than fox news)
Social desirability bias(people will answer questions differently to fox news than the new york times)
 

Vic

Elite Member
Jun 12, 2001
50,415
14,303
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Every individual poll, taken by itself, is completely worthless. You have to take the aggregate and follow the trends.
 

winnar111

Banned
Mar 10, 2008
2,847
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Shrug. All this means is Obama might win 300 EV instead of 350; doesn't change much.

That rustling is investors cashing in any long term gains you can before the tax hammer drops.
 

techs

Lifer
Sep 26, 2000
28,561
4
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I just read that McCain trails Obama by the same amount Gore trailed Bush at this point.
And we all know that it turned out to hinge on few Florida votes.
 

First

Lifer
Jun 3, 2002
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Originally posted by: winnar111
Shrug. All this means is Obama might win 300 EV instead of 350; doesn't change much.

That rustling is investors cashing in any long term gains you can before the tax hammer drops.

And funnily enough Republican presidents have been raising taxes since Reagan, save for the current bum in office.
 

First

Lifer
Jun 3, 2002
10,518
271
136
Originally posted by: techs
I just read that McCain trails Obama by the same amount Gore trailed Bush at this point.
And we all know that it turned out to hinge on few Florida votes.

You are wrong in the extreme and/or you can't read.
 

jackace

Golden Member
Oct 6, 2004
1,307
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A 200 level statistics class in any decent university will explain why polls are so different. They are heavily influenced by how you collect your data and any assumptions you make about "voters". Then you have the margin of error which in most polls is +-3%.