by first, constructing a sample of registered voters, and second, applying a series of screening questions to determine which of those voters is likely to vote. That's what Messina was talking about in his argument that "traditional polling" was "broken" -- the Obama campaign's theory throughout the election was that pollsters using the kinds of likely voter screens that have worked in the past (like Gallup and Rasmussen) would be wrong this time. The lesson we learned, at least this year, is that Messina was right and the traditional, professional pollsters were wrong -- and that the nature of Obama's coalition made the application of likely voter screens particularly likely to affect the accuracy of the polls. But determining which voters are likely to vote is the part of polling that is most inherently subjective and least scientific. Moreover, pollsters are often not very forthcoming about how they make these determinations, and when they release a poll, so sometimes the best you can do is compare the number of registered and likely voters in the sample. As a result, a certain amount of deductive work is required to figure out why some polls give different results from others. There's only so much we can know from the outside, but it appears that pollsters like Gallup and Rasmussen were, for much of the cycle, using likely-voter screens that made traditional assumptions about who would make the effort to vote -- and those assumptions just didn't hold this year, as illustrated by