Dissent Networks of the Supreme Court

Although I have blogged a lot about my New York experiences in the last two years, I have rarely blogged about what I am really here for: living it up in the party capital of the US .... uh .... no, I mean working like crazy at grad school. But I've done some things which I have found really interesting. So I'm going to post a couple of results from some recent work.

This semester I did a great course on Network Theory, or the study of complex systems represented as theories, under Professor Dragomir Radev from the University of Michigan. What I liked about this course is how it applies to so many fields: computer science, of course, but also biology (protein-protein interactions), politics (committee structure of the US House of representatives) or linguistics (word networks like WordNet)

As a final project for the course, I wrote a paper called Dissent Networks in the US Supreme Court. Based on data from the Rehnquist I court (1986-1995) I linked the Supreme Court justices based on the extent to which they dissented together against the majority opinion in the court rulings. Then I ran a clustering algorithm on the network to cluster it into different blocs. Here is an example of the work, from the year 1989:
The abbreviations for the Justices are Ma=Marshall, Br=Brennan, Wh=White, Bl=Blackmun, Re=Rehnquist, St=Stevens, O'C=O'Connor, Sc=Scalia, Ke=Kennedy. The size of the nodes represents how much the justices dissented altogether, and the strength of the lines shows how much they dissented with each other. The colours represent the dissent blocs as identified by the clustering algorithm. The clustering is what is interesting: based on the dissent links, very clear blocs emerge. For 1986-1989 it was pretty much the same picture as the one shown above: heavily dissenting veteran justices Thurgood Marshal (the first black justice on the court) and William Brennan from previous liberal courts joined with their younger colleagues Stevens and Blackmun to form a consistent dissent bloc in a conservative court lead by Chief Justice William Rehnquist, who was appointed by Ronald Reagan.

Things get really interesting after this, because the older justices retire and are replaced by conservative nominations by first Reagan and then George Bush, the dissent bloc falls apart. Here is the situation in 1992, look at how different it is:
It is only after the nomination of Justices Ruth Ginsberg and Stephen Breyer by Bill Clinton in the mid-1990's that the clear dissent bloc re-emerges, although in a weaker form.