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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the last three elections

Saturday November 10, 2012

Filed under: politics,statistics — jackman @ 1:59 pm

I tweeted earlier that the correlation between 2012 and 2008 state-level, Democratic, two-party vote shares is .982. Take out (the outlier) DC and this goes down to .976.

Here’s another look at the data, comparing 04, 08 and 12. More on this later (as well as overlaying the national two-party vote shares), but we have stories that go along with Alaska, Hawaii, New Jersey (!), Utah, over these three elections.

What is striking is how the swing stayed small where Obama and Co. needed it to stay small. Big swings against them in Indiana and the South didn’t matter.

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Two downloads from my poll-averaging model

Thursday November 8, 2012

Filed under: politics,statistics — jackman @ 5:33 pm

I’ve had numerous requests for various outputs from my model, so I’ll put them up here.

1. Forecast win probabilities for Obama, by unit, by day. These were the quantities also requested by a group of researchers working at Penn, who will use Brier scoring to assess various probabilistic forecasts of the state-by-state outcomes.

A summary of how well the final (Election morning) state-by-state probabilities performed is shown in the attached graph, which plots Obama 2-party vote share (using data from this afternoon from AP) against the probabilities from my model.

The probabilities are the data I’ve presented in this graph:

The data themselves are here (CSV). The final set of probabilities also appear in the file I link to below.

2. State level predictions, Obama 2-party vote share, plus uncertainty assessments. The comparison with actual state-level outcomes appears in the following scatterplot (the diagonal line is a 45 degree line).

Data here (CSV). One of the columns is the final probability of Obama win, if you are looking for that.

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Australian vs US election admin: not even close.

Saturday November 3, 2012

Filed under: Australian Politics,politics — jackman @ 11:55 am

It isn’t really a fair comparison, since there isn’t such a thing as “US election administration.”

Rather, like national elections themselves, there is a “rich tapestry” (um “wild riot”?) of state and county level election administration systems in the United States, with much variance in law, technologies, budgets, professionalism, partisanship and traditions.

Annabel Crabb takes a light-hearted look in this SMH piece, teasing a Foreign Correspondent story (ABC TV). I’ve been banging on about this for years to Oz journos etc; Australians ought to better understand and appreciate the minor admin miracle that the AEC is.

Peter Brent (@mumbletwits) wrote a PhD dissertation (big PDF) that took a solid look at the historical background, how Australia came to get something like the AEC (inter alia). I’ve long thought “it wus compulsory voting wot dun it“: that professional, standardized, centralized, election admin is a consequence of enacting a national-level compulsory voting statute in the 1920s. But last time we corresponded on this (a comment on my blog) Peter said his dissertation research found that Australian election admin was headed in this direction ahead of CV.

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Why David Brooks is like another musty old tory…

Friday November 2, 2012

Filed under: general — jackman @ 4:58 pm

At the risk of flattering Brooks, his rant re Nate and probabilities did remind me of Edmund Burke howling at the moon:

…the age of chivalry is gone.

That of sophisters, economists; and calculators has succeeded; and the glory of Europe is extinguished forever.

from Reflections on the Revolution in France.

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