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The Democratic Strategist

Political Strategy for a Permanent Democratic Majority

Do the Tighten Up, Part II

The latest data point being seized on by conservatives to support the idea that the presidential race is “tightening” is yesterday’s results for the Investors Business Daily/TIPP national tracking poll, which had Obama’s lead down to 1.1%. This is supposed to be especially important because IBD/TIPP came closest to predicting the 2004 results.
Nate Silver, bless his pointy little head, noticed a really bizarre internal finding in that poll: it showed McCain beating Obama by a 74-22 margin among 18-24 year-old voters. He proceeds to blow up the whole survey:

Suppose that the true distribution of the 18-24 year old vote is a 15-point edge for Obama. This is a very conservative estimate; most pollsters show a gap of anywhere from 20-35 points among this age range.
About 9.3 percent of the electorate was between age 18-24 in 2004. Let’s assume that the percentage is also 9.3 percent this year. Again, this is a highly conservative estimate. The IBD/TIPP poll has a sample size of 1,060 likely voters, which would imply that about 98 of those voters are in the 18-24 age range.
What are the odds, given the parameters above, that a random sampling of 98 voters aged 18-24would distribute themselves 74% to McCain and 22% to Obama?
Using a binomial distribution, the odds are 54,604,929,633-to-1 against. That is, about 55 billion to one.
So, there is an 0.000000002% chance that IBD/TIPP just got really unlucky. Conversely, there is a 99.999999998% chance that one of the following things is true:
(i) They’re massively undersampling the youth vote. If you only have, say, 30 young voters when you should have 100 or so in your sample, than the odds of a freak occurrence like this are significantly more likely.
(ii) Something is dramatically wrong with their sampling or weighting procedures, or their likely voter model.

Meanwhile, back on Planet Earth, a huge batch of new state polls yesterday gave John McCain what Silver called his worst polling day of the year.

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