State polls show a bigger lead for Obama than national polls do

Consider that as of Tuesday afternoon, President Obama’s lead in the RealClearPolitics average of national polls was 1.3 percentage points over Mitt Romney.

But Mr. Obama led by a mean of 3.5 points in the RealClearPolitics averages for the 10 states (Ohio, Virginia, Florida, Pennsylvania, Colorado, Iowa, Nevada, Michigan, New Hampshire and Wisconsin) that are most likely to determine the election outcome, according to our “tipping point index.” If the list is expanded to cover the five other marginally competitive states where RealClearPolitics calculates a polling average — Arizona, Minnesota, Missouri, New Mexico and North Carolina — Mr. Obama’s lead averages 3.1 points, according to the numbers. …

Perhaps the most common assumption is that if Mr. Obama is performing comparatively well in swing state polls, he might have some advantage in the Electoral College in relation to the national popular vote. Perhaps we are on track for a split outcome, as we had in 2000, but this time with Democrats benefiting from the idiosyncrasies of the Electoral College.