On the basis of two papers and because it is completely obvious, we (meaning me, Justin, and John) predict that Elena Kagan will get confirmed to be an Associate Justice of the Supreme Court. But we also want to see how close we can come to predicting the votes for and against.
We actually have two sets of predictions, both using the MRP technique discussed previously on this blog. The first is based on our recent paper in the Journal of Politics showing that support for the nominee in a senator’s home state plays a striking role in whether she or he votes to confirm the nominee. The second is based on a new working paper extending “basic” MRP to show that senators respond far more to their co-partisans than the median voter in their home states. Usually, our vote “predictions” do not differ much, but there is a group of senators who are predicted to vote yes for Kagan with a probability around 50% and the two sets of predictions thus differ for Kagan more than usual.
The other key factors that enter into the models (which build on the work of Cameron, Segal, Songer, Epstein, Lindstadt, Segal, and Westerland) are senator and nominee ideology, party and partisan control, presidential approval, nominee quality, and nomination timing.
The bottom line? The older model predicts nine Republican defections (votes for Kagan) but the newer model breaking down opinion by party predicts only five. Ten Republicans straddle or push against the 50% mark for point predictions.
Median state-level support for Kagan is approximately that for Alito, and about nine points higher than that for Sotomayor. Median state-level support for Kagan among Republicans is about 12 points higher than for Sotomayor. On the other hand, Obama’s approval is definitely lower. So far, we have only one national poll to work with (which we thank ABC for), but we will update our data and “predictions” later when other poll data become available. We do not yet have Jeff Segal’s official scores for quality and ideology so are currently fudging these a bit (using the same scores as for Sotomayor).
First, here is the distribution of opinion across states by party groups (using an extension to the MRP technique to generate not only opinion by state using national polls, but opinion by party by state):
Next, here are the predicted probabilities of a positive confirmation vote for Republican senators (Democrats are all predicted to vote yes):
If only Lindsey Graham would do the right thing and vote no…