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By Jay Cost

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Interesting Internals in the ABC/WaPo Poll

A few days back, I saw that Clinton web video called "Caucusing Is Easy." You probably saw it, too. Anytime Bill does something, it gets noticed:

At the time, I thought it was a bit strange - insofar as it did not cohere with the conventional wisdom that Clinton and Edwards were the ones winning the support of veteran caucus voters, and Obama was winning over newer "voters." It seemed to me that this kind of video would be something to expect from Obama.

That last paragraph sports some important scare quotes - because newer voters often turn out not to be voters at all. Systematic survey evidence has picked this up - and it conforms with anecdotal accounts. Remember Nader's huge rallies in 2000? How about Dean's in 2004? This is why videos like this get made: young people are unreliable voters, and often need to be charmed into voting. Many pundits have speculated that the young supporters of Obama might be his Achilles' heel - as they are sufficiently motivated to come out and see him on a cold fall day, but not motivated to support him on caucus night. The former has some curiosity value. The latter? Not so much.

So, it surprised me that Clinton was the one creating a "hip" video about caucusing. Then I saw this in the Washington Post's write-up of its latest poll:

Overall, the poll points to some strategic gains for Obama. His support is up eight percentage points since July among voters 45 and older -- who accounted for two-thirds of Iowa caucus-goers in 2004. He also runs evenly with Clinton among women in Iowa, drawing 32 percent to her 31 percent, despite the fact that her campaign has built its effort around attracting female voters.

And despite widespread impressions that Obama is banking on unreliable first-time voters, Clinton depends on them heavily as well: About half of her supporters said they have never attended a caucus. Forty-three percent of Obama's backers and 24 percent of Edwards's would be first-time caucus-goers. Previous attendance is one of the strongest indicators of who will vote.

First off - WaPo does a good job of splashing some cold water on the statistical significance of the topline results. The margin of error on this poll is +/- 4%, so a 4 point lead for Obama is not statistically significant. However, statistical significance is conditioned by the number of observations. It has a lot in common with a simple computation of the standard deviation - which has the number of observations in the denominator. As the number of observations decreases, the standard deviation increases. It's the same basic premise for the margin of error.

So, when you are dealing with a subsample of the whole poll - say, voters 45 and older - the margin of error increases. I'd have to run a statistical test to confirm it (and the internals of the poll just do not provide the data to enable it) - but my intuition is that Obama's gains with older voters is not outside this increased margin of error. An 8 point difference between this poll and the July poll would be significant with the topline results, which are based on 500 observations - but probably not with a subsample of about 200 observations. WaPo was thus wrong to identify this as a "strategic gain" for Obama. It could very well be a sampling anomaly.

That being said - there are still some interesting inferences that we can make without running an undue risk of Type I error (i.e. wrongly concluding that something is significant when in fact it is not). The poll found Clinton and Obama relying on first time voters by about equal measure. The difference between their new supporters is not statistically significant - so the conventional wisdom about how Obama is relying on new voters more than Clinton does not hold. Accordingly, we have explained how Hillary's campaign could coax Bill onto a NordicTrack.

What probably does hold is the argument that Edwards is relying on new voters less than Clinton and Obama. The breakdown is basically 50/43/24. That is, (about) 50% of Clinton supporters are new, 43% of Obama supporters are new, and just 24% of Edwards supporters are new. Again, I would have to see more data than what ABC News/WaPo is providing - but my intuition is that the difference is statistically significant. Edwards is relying less on new voters.

This conforms with what Ana Marie Cox wrote last week in Time. Most of Edwards' supporters are reliable caucus goers. This might give us some clues about what to expect on caucus night. If attendance at the caucus is greater than what it has been in years past, that might bode well for Clinton and Obama. If it is equal to or less than what it has been, that might bode well for Edwards.

Another point on Clinton v. Obama. Clinton is splitting the female respondents evenly with Obama. She pulled in 31% of female respondents. He pulled in 32%. It is surprising to me that Clinton is not pulling in more females in this poll, given the tone of her campaign of late. These results make Mark Penn's promise to pull in Republican women seem like rhetoric designed to win over Democratic voters hungry for a victory.

For comparative purposes, I would note that the recent CBS News poll also found no statistically significant difference between Clinton and Obama among first time and long time caucus attendees. It also seems not to have found a statistically significant difference between them on levels of female support (although Clinton does lead this category by 12%, it is such a small sample that I suspect the lead is statistically insignificant), and levels of support among voters aged 45-65. However, it did find what appears to be a statistically significant difference on levels of support among voters 65 and older, though there is a tie between Clinton and Edwards among voters of that age. [Again - I'm "spitballing" these conclusions of significance because none of these polls ever give you the data you need to draw more assured conclusions.] So, all in all, I would say that the results of the ABC/WaPo poll roughly conform with the results of the CBS poll.

Now - it is important to remember that there are boundaries that we have to obey when drawing inferences from these Iowa polls. I wrote about this last week. Care is important because the Iowa Democratic caucus is a poor fit with the way polls are conducted. I am pretty sure that I have managed to color within these lines in this write-up - but we need to be careful.

-Jay Cost