Here’s Jaci & my paper for the Midwest 2011, Party Aggregation & Political Consolidation in the American States. I think it needs a snappier title, but the analysis is good. The updated version (probably due post-Midwest in the summer) will have measures of social heterogeneity (birthplace fragmentation I think), a longer time series, and hopefully more states (although the ones we have are a giant pain in the neck as it is).
