I’m allergic to math, but even I can understand why Barack Obama’s eight-point lead in the Zogby tracking poll is bigger than it looks.
Zogby has consistently had John McCain doing better than in many other polls. As Nate Silver explains, it’s because Zogby weights party affiliation based on exit polls from the previous election.
So if the electorate is more Democratic today than it was in 2004 — and it is, by quite a bit — then Obama’s lead is actually understated by Zogby. That is, if the tracking poll is accurate in the first place, which is always a question worth asking.