This study measures a nominee's ideology according to the Segal-Cover score, a 0-1 system that uses major newspapers' editorials to gauge perception of a nominee (0 is the most conservative). The graph below expands on Tuesday's analysis of nominees since the Franklin Delano Roosevelt administration.

The green line tracks the average score of nominees serving on the court since 1950, the first year the entire court was made up of justices in the S-C system. The chart begins a shift from liberal to middle-of-the-road to conservative at the same time Republican presidents began to make most of the picks, starting with Richard Nixon.

The trend underscores the notion laid out by several SCOTUS observers since Justice David Souter announced his retirement: that no nominee President Obama was likely to pick would shift the court's conservative slant. In a review of the high court's term today, the Washington Post describes "a patient and steady move to the right led by Chief Justice John G. Roberts Jr., one that is likely to continue even if" Obama "is successful in adding Judge Sonia Sotomayor to the high court -- and perhaps two others like her."

Since the scores are based on editorials written before the nominee is confirmed, the system is by no means foolproof. Assumptions or bias in the media could skew the results, and justices sometimes change while serving. John Paul Stevens and Harry Blackmun scored as safely conservative nominees, but both became known as strong liberals. Souter himself scored as more conservative than either Sandra Day O'Connor or Anthony Kennedy but later joined Blackmun and Stevens in the court's liberal bloc.

Jeffrey Segal, a political science professor and half of the duo that developed the system, told NationalJournal.com last month that the ideology ratings do "an excellent job of predicting justices' overall liberalism or conservatism once they're on the Supreme Court." He said he's found a 0.79 "correlation coefficient." This means that you can predict the justices' overall voting behavior "fairly accurately simply by knowing their ideology," Segal said.

Segal has said Sotomayor would likely score near Ruth Bader Ginsburg's 0.68. That's comfortably in the liberal side but not far from the median in the S-C system.

Editor's note: This is the second in a series of posts examining historical data from a database compiled by Northwestern law professor Lee Epstein and her colleagues. Check back next week for more context and analysis on Sotomayor.