Are national polls AND Ohio polls both right?

No way, says Josh Jordan.  Excellent read, so please check it out.  Excerpt:

In Ohio, Republicans tend to outperform their share of the national vote: In the last six presidential elections, only in 2004 has the Republican candidate performed worse in Ohio than he did nationally, and even that was a difference of only 0.3 percentage points. In the other five elections, the GOP candidate outperformed his margin of the national vote by an average of 3.1 percentage points. While it’s clearly possible for Republicans to perform worse in Ohio than nationally, it is very difficult to imagine a scenario where there is more than a point difference between them based on past elections. History would suggest Romney could not be up 2 points nationally while being down 2.1 in Ohio, which would mean that Republicans would be under-performing in Ohio by more than 4 points.
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Both of these points suggest that it is more likely that either the national polls or the Ohio polls are wrong, rather than the possibility that both can be right. There is a big reason for this discrepancy: the partisan makeup of the Ohio polls.

As mentioned above, in current Ohio polls, Democrats have a party-ID sample advantage of 6.3 points. In 2008, Democrats had a 5-point turnout advantage in Ohio. That means that while national polls have the turnout advantage down 2.6 points, in Ohio it has actually increased 1.3 points. It is almost impossible to conclude that while the nationwide party-ID advantage of Democrats has dropped since the wave election of 2008, Ohio has actually increased over the last four years.

If that’s not enough, the Ohio polls have actually become more Democratic since the post-DNC polls that gave Obama the significant bounce that led many pundits to declare Romney’s chances in Ohio DOA. Of all Ohio polls from September 7 to September 19, Obama held an average lead of 4.2 points, with a Democratic party-ID advantage of 5.7 points. Today Obama leads by 2.1 points, with a party-ID advantage of 6.3 points. In the last month, while Romney has had surges in polls all over the country, the polling in Ohio has actually found more Democrats even while Obama’s lead was cut in half. …

Um…unlikely, to say the least.  Case in point: a new PPP (the Daily Kooks’) poll shows Oba-Mao with a +4 lead over Romney in OH…with a D+8 sample, even bigger than the big blue wave of 2008 (and +9 bigger than the R+1 that turned out during the red wave of 2010…so a 9% swing ONLY TWO SHORT YEARS AFTER the nation rebuked Obama? Really?).  So with an unrealistic +8 sample advantage over Republicans, the best B.O. can do is to only get HALF of those?

B.O. can’t win without Ohio.  Romney CAN, though it’s hard to imagine that he’d lose Ohio but pick off other “firewall” states needed to offset the difference (WI and either IA, NH, or NV, assuming CO continues its pro-Romney trend).

In the end, the only poll that matters is the one AFTER the votes are in.  But regardless of who wins, it will be a fun exercise to go back and look to see which pollsters were right and wrong, and see if they explain themselves.