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"Outlier"

Topics: 2008 , Divergent Polls , The 2008 Race

Two weeks ago, a new ABC News/Washington Post poll showed Hillary Clinton "surging:"

She has 53 percent support in the latest ABC News/Washington Post poll, up 12 points from early last month, vs. 20 percent for Barack Obama (down seven points to his lowest of the year), and a stable 13 percent for John Edwards.

In a blog post on that poll, I noted the dramatic interpretation of these results in various corners and then looked at how the poll compared other results (based on trial heats omitting Al Gore as an option). I wrote:

[T]he 53% result for new Post/ABC poll is more of an "outlier" from the regression trend line than any poll conducted this year (it's the purple dot at the extreme top right of plot area). At 53%, the polls estimate of Clinton's support falls a full ten percentage points higher than our current estimate of the trend (42.5%) even without Gore in the race.

Since then, six new national polls have been released, and all but one** show support for Clinton above the 42.5% trend estimate we reported ten days ago. With the addition of those new polls, the trend line below, based on trial heat results that do not include Gore now shows an expanding Clinton lead, with her support increasing roughly 3 percentage points since August.

AUS2TopzDems071016sml.png

The 53% result for Clinton on the ABC/Post poll remains on the high end of support for Clinton compared to the trend line, but is no longer "more of an outlier" than various other polls conducted earlier in the year.

ABC's Gary Langer also sent a table this morning to point out something I overlooked two weeks ago. I've reproduced it below (splitting it into two parts to better fit this space). He first reproduced the results as reported by the pollsters - the same results plotted in our chart above:

10-16%20recent%20dems.png

Notice that the ABC/Post result for undecided (2%) is lower by far than any of the other results in the table. That difference is not unusual, in that the ABC/Post poll typically shows a smaller "don't know" result than other polls. Langer then recalculated each result as a percentage of those with a preference. Calculated this way, the ABC/Post results look much closer to the average of all six poll and not at all like an "outlier."

10-16%20without%20undecided.png

So point taken.

But let's also remember that the typically lower than average undecided on the ABC/Post poll did not produce a similarly discordant estimate for Clinton in early September. Their September 4-9 survey put her support at 41%, within a percentage point of our trend estimate at the time. So we cannot explain away the apparently dramatic 12 point increase as an artifact of a small undecided.

Finally, about my speculation twelve days ago:

Of course, we do not yet know whether this poll is really a statistical outlier. Other polls have obviously been showing a more gradual increase in her support recently, and it is still theoretically possible that Clinton's support suddenly lurched up ten points last week...

So we will wait and see. But I'll wager that a month from now the real trend will not look nearly as dramatic as the one suggested by yesterday's news.

A month has not yet passed and the trend line for September might still change, but I stand by my wager.

**The Insider Advantage national poll of Democrats, not included in Langer's chart, looks far more deserving of the "outlier" label if only because of its huge 23% undecided produced by informing respondents that "no opinion" is an option.

 

Comments
hwc:

InsiderAdvantage tacitly suggested that their first national poll may be an "outlier" by running a second poll a week later. The second poll showed Clinton jumping from 31% to 43%, despite the fact that the second poll included Gore. I doubt that Clinton's actual support jumped 12 points in seven days.

BTW, thank you so much for the Gore-less charts. If you could provide a more accessible link, that would be great. We've reached the stage where including Gore is obscuring the nature of the actual race among the actual candidates.

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cnn:

Mark,

CNN has just released a new poll. Clinton is cracking 50.


Clinton 51
Obama 21
Edwards 15

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Is it be possible to show trend lines for the "undecideds"? It would be neat to see how the percentage shrinks as we get closer to actual votes being cast for candidates.

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Mike:

I'm voting for Obama. I don't have a land line, so I won't be showing up on any of your polls.

Oh, and there's millions more out there, just like me. See you at the polls.

-Mike

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digbydolben:

I don't have a land line either, and I'm voting for Obama, as well. Another thing you're not considering: many of us voting for Obama are not doing so on account of ideology--his or ours. The Republican candidates are married to failing policies and many centrist Republicans like me know it, and are willing to cross party lines to vote for Obama because he's HONEST and NON-IDEOLOGICAL, and, instead, pragmatic and respectful of centrist conservative ideas like mine. Also, he's AGAINST THE WAR, and Clinton will continue "neo-conservative" foreign policies and the "unitary executive" style of leadership, and we know it. Why does this spell a "sleeper" victory for Obama? Take a look at all the important early primaries. They're "open" primaries--ones in which Republicans like me can cross party lines and vote for Obama. In these polls, you're only paying attention to registered Democrats and Independents, rather than to libertarians and centrist Republicans like me. WE are the ones who are going to surprise you in Iowa, New Hamphshire and South Carolina. And, then, if Hillary takes the nomination away from Obama--the only Democrat who, with a chance of winning, promises real change, we will either stay home on election day or vote for Ron Paul, the likely Libertarian candidate. That woman is a neo-fascist, like Bush, and the libertarian-leaning Democrats and Republicans are no more going to vote for her than for one of the Republican war-mongers.

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bill:

Mike get real and think white nobodys going to vote for a caucasian asian over an experienced and highly world respected ready to be prez. like hillary

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