First the good news:
A new NEWSWEEK Poll shows that he has a substantial double-digit lead, 51 percent to 36 percent, over McCain among registered voters nationwide.
There's no doubt that this poll accurately reflects Barack's bounce, and there's no doubt that he's leading.
As for whether he's actually leading by 15 points -- color me skeptical.
Remember that there's an element of dumb luck in every poll, measured by margin of error. (There's another type of error that comes in with survey methodology and likely voter modeling, but that's a different story.)
This poll's margin of error is 4 points, but that doesn't mean that the poll will never be off by more than 4 points. What it means, technically, is that the poll will accurate within 4 points 95% of the time (2 standard deviations). In other words, 5% of the time, it will be inaccurate. (Even if it's outside the 4 points however, it's more likely to be closer to the 4 points than further.)
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For context, I took a look at all the 2004 national polling that I could get my hands on -- a total of 270 polls, including Rasmussen's weekly averages.
Kerry's largest lead in any poll was 12 points and came in CNN/USA Today/Gallup poll taken in the middle of February, right about when he wrapped up the nomination.
Bush's largest lead in any poll was 16 points and came in a Pew Research survey from September 8, right after the GOP convention.
As for Newsweek itself, the largest lead they showed for Kerry was 7 points after the Democratic convention, and the largest lead they showed for Bush was 11 points after the GOP convention.
So I think we can fairly say that this poll absolutely confirms Barack Obama's lead, but I also think it would be a mistake to assume that his lead is actually 15 points wide.
© Jed Lewison