Polarization is Real (and Asymmetric)
http://voteview.com/blog/?p=494
The recent outburst of scholarly and popular interest in political polarization has attracted attention to the methods we use to measure this phenomenon. One frequently voiced concern (see a recent column by Sean Trende) is that Congress may not have polarized as we have claimed in publications and blogs stretching as far back as 1984. The concern is that the meaning of ideological (NOMINATE) scores are tied to the legislative and historical context of the roll call votes that are used to estimate them. For example, the content of roll calls votes cast by members of 90th Senate that dealt with the Vietnam War, civil rights, and funding for LBJ’s “Great Society” programs are quite different than those votes cast in the current Senate. Thus, being the most conservative Senator (with a score of 1.0) in 1968 would mean something different than having an identical 1.0 score in 2012.
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