Today's Polls: Obama Now Better than 2:1 Favorite
from The Plank by Nate Silver
Let's not equivocate too much here. Over the course of the past several days, there has been a rather dramatic shift in this election toward Barack Obama. Our trendline estimate, which is engineered to be fairly conservative, registers the swing as equaling roughly 4 points over the course of the past week.
Changes of this velocity are unusual outside of the convention periods and the debates, especially in close elections. It took John McCain about 60 days and tens of millions of advertising dollars to whittle Obama's lead down from roughly 5 points at its peak in early June, to the 1-point lead that Obama held heading into the conventions. Obama has swing the numbers that much in barely a week.
Of course, we never really were entirely outside of gravitational field of the conventions, and probably at least half of this bounceback for Obama is merely the more-or-less inevitable consequence of McCain's convention bounce ending. But the fact is that Obama is in a stronger position now than he was immediately before the conventions. We now have him winning the election 71.5 percent of the time, which is about as high as that number has been all year.
There are two reasons why that number is as high as it is. Firstly, we are more than halfway through the penultimate month of the campaign, so even relatively small leads are fairly meaningful. But secondly, Obama has developed a structural advantage in the Electoral College that is understated by the popular vote margin. If we break the election down into its four fundamental scenarios, it looks like this:
62.5% Obama wins Popular Vote and Electoral College
0.7% Obama wins Popular Vote, loses Electoral College
27.8% McCain wins Popular Vote and Electoral College
9.0% McCain wins Popular Vote, loses Electoral College
Obama is roughly a 63/37 favorite to win the popular vote -- numbers that ought intuitively to look pretty reasonable for a candidate who holds a 2-point national lead fortysome days before the election. It's that 9 percent of the time he wins the Electoral College while losing the popular vote that make his 2-point lead much more robust. If the states maintain their positioning relative to one another -- and they may well not -- Obama probably has about a 1-point cushion in which he'll remain the favorite to win the Electoral College even while losing the popular vote.
http://blogs.tnr.com/tnr/blogs/the_plank/archive/2008/09/19/today-s-polls-obama-now-better-than-2-1-favorite.aspx
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