roll calls, ideal points, 112th Congress

June 29, 2011
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(This article was first published on simon jackman's blog » R, and kindly contributed to R-bloggers)

Now that classes are over, I took a little time to update my scripts that update the analysis of Congressional roll calls in close to real time.   Links appear at the top of the blog.   As of about 15 minutes ago, we’re up to 77 non-unanimous roll calls in the 112th Senate.   The House has 474 non-unanimous roll calls under its belt.

I’m presenting estimates of legislators’ “ideal points” and 95% credible intervals (from a model that fits just a single underlying dimension to the roll calls) both graphically (House/Senate) and in CSV.  I also present scatterplots (and loess smoothing) of the estimated ideal points against a crude (but useful) measure of preferences in the legislators’ district/state, Obama vote share in the 2008 election (House/Senate). I’ve also got a SVG with rollovers for the dense House scatterplot, using the RSVGTipsDevice package, but the resulting SVG breaks in Chrome.

I’m scraping the roll calls and some meta data from the House and Senate sites, using the parsing in R’s XML package (which I’m finally understanding how to use effectively).   Analysis of the roll calls is via the ideal function in (my) R package, pscl.

Quite aside from the methodology/technology, the substantive story is very much business as usual: zero partisan overlap in the recovered ideal point estimates. About 1 to 1.5 standard deviations of the ideal point distribution separate the ideal points of Democrats and Republicans among districts/states that split 50-50 Obama/McCain in 2008.

The other striking feature of the data is how few Democrats remain in the 112th House in districts where McCain beat Obama: I count 12 such seats.

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