I did a little work on the Coburn amendment rollcall. The vanilla spatial voting model fits the roll call reasonably well; I use all 341 roll calls cast by the 111th U.S. Senate (at least as of this morning when I ran the analysis) to estimate the ideal points, and then look at the fit to the roll call on the Coburn amendment.
The graph (thumbnail below) summarizes the fit, with the curve tracing out the predicted probabilities as a function of estimated ideal point (these come a simple probit regression of the actual votes on the ideal points). The estimated cutpoint — the point where a legislator is indifferent, on average â€” is between the ideal points of Voinovich (R OH) and Murkowski (R AK).
The “surprises” (or deviations from “pure” spatial voting) are show on the graph:
- 5 Democrats voting for the amendment: Baucus, Webb, McCaskill, Bayh, Nelson.
- 7 Republicans voting against the amendment: Bond, Alexander, Cochran, Gregg, Johanns, Cornyn, Burr.
- Voinovich (R OH) is predicted to vote against the amendment (ideal point lies to the left of the cutpoint), but voted Yea.
Snowe (R ME) and Collins (R ME) are to the left of the cutpoint and voted in accordance with the model prediction.
Bayh is up for re-election in 2010, as is Voinovich; for what it is worth, both are in Midwestern states. The splits in the MO and NE delegations are interesting.
In the spirit of trying to explain “errors” here, I’m wondering if any of our political science colleagues engaged in lobbying (seriously). For instance, did the Vandy people email Lamar Alexander? Did the UT/UH/Rice/Texas A&M people contact Cornyn’s office? And a lot of Federal research money finds it way to North Carolina, too (e.g., SAS, RTI, UNC & Duke, etc); Burr (R-NC) voted against the amendment, with an ideal point a long way to the right of the estimated cutpoint. Of course, it would also be interesting to consider cases where lobbying might have failed (McCaskill?).
Conversations with colleagues I was with yesterday (at the NSF!) had the more sensible take on this, probably to chalk it up to “position-taking”; with such a small amount of money at stake, the vote is largely symbolic (were that it were otherwise). That is, this is the kind of roll call that incumbents will add to their respective tallies in campaign statements to the effects of “I voted against waste and fraud n timesâ€¦”