Ranking the Politics of Supreme Court Justices

Supreme Court in Washington, D.C.

Just how conservative is the Supreme Court, anyway? It's a question that has dogged constitutional scholars for years, as they've tried to parse the opaque language and muddled writings of judges moving through the confirmation process. Today's court, headed by John Roberts with seven justices appointed by Republican presidents, is generally considered more conservative than the Supreme Court of the 1950s, for example, when Earl Warren oversaw its unanimous decision in Brown v. Board of Education. But it's hard to compare the current court—and today's justices—with, say, the Burger court of the 1970s, which, with six Republican-appointed justices, decided Roe v. Wade.

John McCain, for one, doesn't seem to want to take any chances. Last week, he joined a long line of Republican presidential candidates who have pushed for a more conservative court when he promised to make Samuel Alito and John Roberts his "models" for judicial appointments.

But how conservative would a McCain presidency make the court—and how conservative is it already? The answers to these questions may be found in a new paper by Richard Posner, a judge who sits on the Seventh Circuit Court of Appeals, and William Landes, a law professor at the University of Chicago, that is now making its way through the academic community. In "Rational Judicial Behavior: A Statistical Study," Posner and Landes use a database that includes the political background and voting records of the past 70 years of Supreme Court justices—who appointed each justice and how the justices decided every case—to come up with a ranking, from most conservative to least conservative, of the 43 justices who have served on the court since 1937.

Their conclusion: Four of the five most conservative justices to serve on the Supreme Court since Franklin Roosevelt, including Roberts and Alito, are currently sitting on the bench today. Justice Anthony Kennedy, another current Republican appointee, is ranked No. 10. (The table has a full list.) Justices Ruth Bader Ginsburg and Stephen Breyer, the two current justices nominated by Democratic presidents, are among the 15 "least conservative" justices of the past 70 years. Thurgood Marshall, who became the first black Supreme Court justice when he was appointed in 1967, has the most liberal voting record on the list. Clarence Thomas, the second black justice, who was appointed to the court in 1991, is ranked the most conservative.

NUMBER OF CONSERVATIVE VOTES ON U.S. SUPREME COURT, 1937-2006

These findings may not come as a surprise to political scientists, who have devised a range of techniques over the years for calculating judicial nominees' political ideologies, often based on their records before joining the Supreme Court. But Posner and Landes have taken their research a step further, examining the actual voting records of justices while they were sitting on the bench. To do this, they've relied on a database created by Harold Spaeth, a political scientist at Michigan State University, which codes each vote made on the Supreme Court between 1937 and 2006 as either "liberal," "conservative," "mixed," or "both." If a justice votes in favor of a defendant on a criminal procedure case, that vote is considered "liberal." If the justice votes against the plaintiff in a civil rights case, the vote is considered "conservative."