(original version released on temporary site; comment thread)
Yesterday I wrote a long piece on why national polls paint a different picture from state polls, despite the fact that they use very similar methods. Here’s the ten-cent version – the central argument.
Imagine for a moment that national and state polls use exactly the same methods (not exactly true, but close enough). Historically, pollsters as a group do well. But they aren’t perfect. In 2000-2008, national-poll medians missed the final outcome by 0.3%, 1.4%, and 2.5%, despite the fact that perfect methods would have missed by 0.6% on average. So there’s a large systematic error. How would this affect one’s snapshot view of the national and state race?
This year, the national race is close. A systematic error of 1-2% would make it hard to accurately determine who was in the lead nationally. But state races are usually less close. Even Ohio, a critical swing state, has a median of Obama +3.0 +/- 0.5%, a lead that would not be altered by that systematic error. Indeed, at the moment only two states are within range of flipping in such a way: Virginia and Florida. The likely outcome of the other 49 races would still be determined correctly. Across the country, the Presidency is decided by winner-take-all elections. Therefore our Meta-Analysis of State Polls is likely to come closer tothe correct result than national polls. In coming days I’ll combine the two to come up with a final prediction of the popular vote margin.
I should say that for similar reasons, the U.S. system of electing a President is more fraud-proof than a simple popular vote. Even if there were voting error in one state, the effects would be contained there, like flooding on a compartmented ship. Without the Electoral College, every time there was a close national race we’d have the Florida 2000 dispute (Bush v. Gore) in every precinct in the country. Blech.