Statistics require attention to detail. Early Tuesday morning, with the Pennsylvania primary coming up, the idea of predicting the outcome based on a simple linear formula built from regression data on race of the states having voted up to that point came to me. I pulled my data from my email account since I wasn't at home at the time. Anyway, I didn't save the equation after I plugged in the Pennsylvania numbers.
When I recreated it at home this morning, I came up with a different result--Hillary winning by 4.4 points, 52.2%-47.8%, instead of 8 points as I'd said earlier. After toying around for a bit, I found the mistake. I took the white and black percentages as a total of all voters, and then multiplied it by the white+black total (.96), to come up with Obama's share. The last step isn't needed. So the polls were more accurate.
I'm really sorry for the carelessness. It's why doing things at home without pressing time constraints is a much better way to go (that's where I almost always do my blogging).
Hillary's better performance than the crude equation predicted likely comes from news about Obama over the last several weeks being worse for him than news about Hillary has been for her. Also, most of those sitting on the fence going into the primary are now voting for Hillary. Before March 4, they'd been voting for Obama. The thrust of the post remains the same--demographics are an anchor, while all the other things that go on comprise the wind, shifting the electoral boat back and forth along its anchor-restricted range at the surface.
The equation used:
Barack's total share = ((((46+[black percentage of voters]*-.28436)*[white percentage of voters])+([black percentage of voters]*.84))+(.33*[Hispanic percentage of voters]))/[1-percentage of remaining voters]