More on asymmetric polarization
Here are some graphs to follow up on this Monkey Cage post.
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UPDATE (Sept 12, 2014)
Here's another graph of the Bailey data, to illustrate the narrowing and moderate cross-time shift of the congressional GOP and northern Democratic ideal point estimates, but a more dramatic leftward cross-time shift in the congressional southern Democratic ideal point estimates.
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UPDATE (Sept 13, 2014)
Here are the do files I used to create a database with Bailey scores and state and party codes for each case (House, Senate). Here is a description of the process that I used to create the do files.
How do you factor in who controls what gets voted on? What does and does make it to a vote is where most politics happens, no?
Hi Carolyn,
You are correct that most of politics occurs outside of the congressional roll call vote, and you have identified a problem for detecting patterns in legislative polarization over time. If the legislative agenda-setters start pushing bills to a floor vote that reflect more consensual policies, then polarization will appear to decrease even through there has been no change in legislative ideal points; moreover, with no ideal point change, polarization would appear to increase if roll call votes start to reflect more controversial legislation.
There's no method, as far as I know, by which the Bailey or DW-Nominate data directly account for the legislative agenda (such as by including legislator committee behavior). Bailey's technique tries to account for changes in the legislative agenda in some way by "bridging" observations across time to try to prevent any narrowing or expanding of the policy agenda from influencing ideal point estimates. But that technique has potential problems, because bridging observations are often volunteered statements and thus are a non-random sample of all potential bridging observations.