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Olympia Snowe retirement: replacement musings, rank ordering

Wednesday February 29, 2012

Filed under: politics,statistics — jackman @ 1:32 am

Using all non-unanimous roll calls cast in the 112th Senate, I find Olympia Snowe (R-ME) to come in as the 3rd most liberal Republican in the Senate. See the plots linked above or here (PDF). Snowe has her Maine colleague Susan Collins and next door neighbor Scott Brown (R-MA) to her left. Details below.

It is a little more interesting to think about what kind of Senator might replace Snowe. The picture below plots ideal points from the 112th Senate against Obama two-party vote share in 2008. Maine went 58-42 for Obama in 2008 — right along side states like WA and MI — and it is rare to find Republican senators from states this “blue”: e.g., Kirk (R-IL) and Brown (R-MA).

Should the Democrats pick up the seat, we might expect a Senator racking up a voting history a la Levin (D-MI), Stabenow (D-MI) or Cantwell (D-WA) or Murray (D-WA), right in the middle of the Democratic pack. I’ve seen some commentary looking at Democratic House members from ME taking the seat. See the voteview take (which utilizes a joint scaling of House and Senate members) and a perspective from Sydney, Australia.

If a Republican wins, I think its tough to say. Johnson (R-WI) is racking up quite a conservative voting history, given how “blue” WI was in 2008. My best bet would be that a Republican replacement would be voting quite similarly to Brown and Collins, right at the far left end of the Republican caucus, but who knows…?

It is straightforward to use the output of the MCMC algorithm in ideal to induce a posterior density (or actually, a posterior mass function) over (a) the order statistic of a legislator’s ideal point; (b) the identity of the legislator occupying a particular rank. All of this assumes that ideal points sit on one dimension (a pretty good assumption in contemporary U.S. roll call data).

The pictures below (click on thumbnails) show the story for the 112th Senate thus far. The model attaches most probability to Snowe occupying rank 56 (about 80%). She is by the most likely contender for rank 56. Brown and Collins are harder to distinguish, but both sit just to the left of Snowe.

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