538.com map

[Mr. Morden]

I love 538's wonderful sensitivity...last week or so, Obama was given a >70% chance to win.  Now it's back to 52%, when nothing fundamental has really changed in the race.

538 doesn't care about the "fundamentals" of the race.  It's just designed to reflect whatever the current polling says.  The polling has shifted noticeably in McCain's direction, so 538 is going to reflect that.  The "percentage chance of winning" isn't really a forward projection of what's going to happen (in the same sense as, say, Intrade).  It's just a computation of the probability of each candidate winning if the voting were to line up with the current poll results, and their respective uncertainties.

[Mr. Morden]

The problem is that this is a prediction of what will happen in November. Look at how fast the race went from McCain +2 to Obama +8. Something could easily happen to throw the race back into McCain's favor. The 15% chance doesn't really seem to be accounting for the fact that the race can change very quickly, and it doesn't take more than a few points change to put it back into a very even race.

538 doesn't care about the "fundamentals" of the race.  It's just designed to reflect whatever the current polling says.  The polling has shifted noticeably in McCain's Obama's direction, so 538 is going to reflect that.  The "percentage chance of winning" isn't really a forward projection of what's going to happen (in the same sense as, say, Intrade).  It's just a computation of the probability of each candidate winning if the voting were to line up with the current poll results, and their respective uncertainties.