Nate Silver on the New Quinnipiac Polls and Why Today's Sping Will Be Wrong

AM Polling Update: Why Today's Spin Will Be Wrong
from The Plank by Nate Silver

Quinnipiac is out with polling this morning in the swing states of Florida, Ohio and Pennsylvania. Barack Obama holds a lead in all three: he's ahead by 7 points in Pennsylvania, and 2 in each of Florida and Ohio. But also in all three states, his lead is diminished from last month, when Quinnipiac had shown him 4 points ahead in Florida, 6 in Ohio, and 12 in Pennsylvania.

The media is likely to focus on the near-term trendline -- one that shows movement toward John McCain within the last month. The last set of Quinnipiac polls were conducted near the peak of Obama's post-primary bounce, and there is no doubt that he has lost a little bit of ground since then.

We like looking at trendlines too. But focusing on only the last month risks failing to see the forest for the trees. Fundamentally, the news is that Obama is ahead in all three states -- two of which are states that Democrats have made a habit of losing. Moreover, if you compare his performance not just to the most recent number, but to all other instances of the Quinnipiac polls -- this is how our model looks at things -- the results are pretty decent for him:

Month FL OH PA
Feb M+2 M+2 O+1
March M+9 O+1 O+4
April M+1 M+1 O+9
May M+4 M+4 O+6
June O+4 O+6 O+12
July O+2 O+2 O+7

This is a weaker performance for Obama than in June, but a better performance for him than in any month but June. Our model weights those two factors, and concludes that the status quo has more or less been preserved. As of last night, our model gave Barack Obama a 68.0 percent chance of winning the election in November. With these polls rolled in, he has a 67.7 percent chance.

There's nothing really dramatic here, in other words. And to the extent there's any news at all, it's that Florida and Ohio continue to move toward one another in the polling, which has a lot of implications for resource allocation going forward.

--Nate Silver

http://blogs.tnr.com/tnr/blogs/the_plank/archive/2008/07/31/am-polling-update-why-today-s-spin-will-be-wrong.aspx