08 June 2009

Judicial Ideology on the U.S. Supreme Court

An empirical ranking of the ideology of U.S. Supreme Court justices since 1937 on a liberal-conservative scale (Martin-Quinn scores) can be found here. Negative rankings are liberal, positive rankings are conservative. An idealized moderate would be ranked zero. In the 2007 term the U.S. Supreme Court justices ranked as follows (first year of service rankings in parenthesis):

Stevens: -1.99 (0.03)
Breyer: -1.63 (-0.51)
Ginsberg: -1.51 (-0.33)
Souter: -1.48 (0.97)
Kennedy: 0.14 (1.15)
Alito: 1.38 (1.4)
Roberts: 1.44 (1.48)
Scalia: 2.71 (1.43)
Thomas: 4.83 (2.73)

Most Justices in recent memory have grown more liberal during their term of service on the court. Justice Rehnquist started at 3.98 and ended at 1.5, for example. O'Connor started at 1.5 and ended at -0.04. Blackmun started at 1.9 and ended at -1.86. Powell started at 1.52 and ended at 0.76. Marshall started at -0.96 and ended at -4.31.

Even Scalia who reached peak conservativism in 2000 at 3.47 has declined every year since then to his current 2.71. Justice Thomas, meanwhile, has just grown more and more conservative during his tenure.

The median justice has been a moderate conservative (i.e. greater than 0 but less than 1.04) in every post-World War II year except from 1962-1968 where the median justice was a moderate liberal (i.e. less than zero but more than -0.85). The median justice when Roe v. Wade was decided (Byron White in 1972) was, ironically, more conservative than the median justice in any other year from 1937-2007.

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