How likely is an electoral vote/popular vote split?

So what’s the bottom line? If the race is close on Election Day — less than a point — there really could be a national vote/electoral vote split. Since the overall tendency is for the Electoral College and popular vote to match up, you wouldn’t give more than 50-50 odds of it occurring. I’d call it about 1 in 3 chance, which just happens to be the number of times we ended up with a split decision in the three races decided by less than a point (although there is an argument that Kennedy lost the popular vote — an argument that does not include conspiracy theories about Chicago vote counting –, but that is a story for another day).

What if the popular vote margin is larger than a point? I think the odds are slim that there would be a disconnect. This year doesn’t really seem akin to other years where we’ve seen large mismatches between the popular vote and where the electoral vote number 270 is located. It’s not a blowout like 1964 or 1972, nor is there a substantial third party presence, as there was in 1968 and 1980.

Still, given the result in 2008, I don’t think that we can completely write off the possibility that Romney could lose the Electoral College even if he were to win by more than a point. Now, 2008 was a borderline-landslide year; this year will almost certainly be decided by a closer margin than that election. It’s also difficult to say whether the discrepancy we noted in 2008 was a result of noise in the data or whether the Obama campaign’s efforts actively created such a split.