Here´s my best Mark Blumenthal impression (I recommend both of his recent posts analyzing PA polls).
The top-line numbers in PA polls have been all over the place for some time now. I just took a few minutes to look through all of the crosstabs and to read Blumenthals analyses and I´ve got a quick guide to reading PA polls.
1) Look at the gender crosstab. This is the most obvious point. More women will vote than men, so Obama had better do at least as well among men and Clinton does among women. There´s a second point to this. As Blumethal concludes and the polls seems to indicate, Obama´s hope for a surprise win comes from improvement among non-college educated white men. Since college-educated men have been fairly stable (and have probably made up their minds), and African-American men ought to be the most stable voting bloc of all in this primary, large swings in the male vote should be due largely to changes among the key group. If Obama´s up around 10 points in a given poll, that´s a good sign.
2) See if Clinton has substantial African-American support. Just like we saw before South Carolina and other states, African-Americans have begun to coalesce around Obama in PA. Still, several polls show Clinton with 20% of the AA vote. It´s not likely that Obama can win under such conditions. Check to see if he´s pulling a general election-esque 90/10 split.
3) If they have religion, look at the Catholics. Obama´s gonna win Prots by a small margin. The polls say that and so does my gut. However, the few polls that actually publish religion crosstabs show his getting crushed by 30 and 40-point margins among Catholics. Obviously, he can´t have that happen and expect to win. And since our important swing group is non-college educated white men, the Catholic question is another tool of indirectly tracking where that group is at any moment. Look to see if Obama is pulling down 40% of the Catholic vote. I haven´t done the math to confirm that´s what he needs, but my gut tells me he can´t win without at least coming close to that.
So, the 3 Keys to Obama Victory (and looking for one in a poll): 1) About a double-digit lead with men, 2) 90/10 split among AAs, and 3) 40% of Catholics.
Happy Poll Reading!