Silver is betting his bias along with the Lib pollsters he swallows that borders on delusional like the rest of the clowns at DU.
For an example. Poll after poll including PPP and PMSNBC polls show very large margins of Indies breaking for Romney. I think the average is about 15% over Obama of all polls taken into account. What did Obama win the Independents vote by in 2008? I recall he won it by 7% to 8% over McCain and about the difference in the presidential 2008 election. If the polls are shown to be correct in a few days, that is about a 22% to 23% Indy swing from 2008 and in favor of Romney.
The liberal pollsters and Silver “think” that the Dims will show up voting at the same rate or even more than 2008, and that the Rs won’t increase their numbers but even be less than in 2008 to include the Independents who are woefully under represented in his analysis. The DUmmies are getting taken for a balloon ride where Silver is the balloon pilot. That balloon is filled will hydrogen gas - soon to be a flaming Hindenburg.