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How Obama won: the swing state swings

Sunday November 11, 2012

Filed under: politics,statistics — jackman @ 1:06 pm

Obama won the 2012 election by keeping the swing small where it needed to be kept small. Just two states changed hands: Indiana and North Carolina, both won narrowly by Obama in 2008.

But consider this. Florida, Ohio and Virginia were all won by Obama in 2008 on margins smaller than the 53.4-46.6 national margin. Obama kept them all in 2012, with swings smaller than the national swing. Details…

Nationally, the two-party swing against Obama is currently -2.11 percentage points: that is, Obama beat McCain in 2008 53.4-46.6; at this stage of the 2012 count he is winning 51.3-48.7.

Let’s look at some key swing states.

And on it goes. Without more of these easier states coming over the line, getting to 270 was a very difficult proposition for Romney. The Romney campaign would have needed some large swings in other battlegrounds to get close.

And Pennsylvania? Forget it. With 20 Electoral College votes you can understand why it is an enticing target. But Pennsylvania was higher up the tree than Iowa, New Hampshire or Colorado, breaking 55.2-44.8 in 2008. Romney won a 2.6 point swing in Pennsylvania (slightly higher than the nationwide swing), but still only half of what he would have needed to win the state.

Indiana was the other Romney pickup. Obama’s 50.5-49.5 victory there in 2008 was a shocker, coming on the back of 10.9 point swing: to understand how big that was, recall that the national two-party swing to Obama was 4.8 points in 2008. Indiana was never on anyone’s battleground list in 2012. Expectations were that Indiana would “revert to type”. Absent any serious attempt to defend the narrow and unexpected 2008 win from the Obama camp, Indiana swung 5.8 points in 2012 (more than twice the national swing) with Romney winning 55.3-44.7.

A similar logic applies to Missouri, which Obama almost won in 2008, falling short by 0.06 of a percentage point, outpolled by McCain by just 3,600 votes. Missouri “reverted to type” in 2012 too, with a 4.8 point swing. In fact, Obama’s 2012 showing is worse than Kerry’s in 2004 (45.1% of the two party vote, versus Kerry’s 46.3%).

Two graphs summarize all this; clicking on each will open a larger version in a new browser window.

The first is a dot plot showing the swings in order. The color shows the disposition of the state in 2008. Two vertical bars show the national swing and no swing. Open plotting symbols for swing states show the swing they would have required to change hands: for North Carolina, the open plotting symbol lies to the right of the actual swing (the swing exceeded Obama’s 2008 margin). Again, note how the swings against Obama come up short in the other battleground states.

Second, a plot of 2012 swing against 2008 result. Shaded regions denote politically distinct regions: (1) Obama retains, where the 2012 swing isn’t enough for the state to fall to Romney, with 27 states in this category; (2) Obama losses, where the swing against Obama is enough for the state to fall to Romney (Indiana and North Carolina); (3) Obama gains (a null set in 2012); and (4) Republican retains, with 22 states in this category. The District of Columbia is excluded from this graph. The size of the plotting symbol is proportional to the state’s Electoral College votes; color indicates 2012 disposition; the national result is shown with a dark point labelled “USA”.

Obama wins the election on the back of that set of states that sit just to the right of the 50-50 threshold on the horizontal axis, but that didn’t drift down on the vertical “swing” dimension into the “change hands” cone.

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