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.