University of Chicago law professors Thomas J. Miles and Cass Sunstein summarize their effort to determine which Supreme Court justice is most "activist." Rather than look at constitutional cases, or challenges to statutes, they looked at challenges to federal agency actions, judging a justice to be "activist" based upon how often he or she votes to overturn an agency decision. Here is how they describe their approach:

Everyone looks at the high-profile constitutional cases, but to get a real sense of how justices approach their jobs, it's best to analyze the more routine, less-visible cases that are often more important to people's daily lives.

For this reason, we examined all cases in which members of the court, using settled principles, evaluated the legality of important decisions by federal agencies, such as the Environmental Protection Agency, the National Labor Relations Board, the Occupational Safety and Health Administration and the Food and Drug Administration.

We used clear and simple tests to code the decisions of these agencies as either "liberal" or "conservative." For example, we counted an environmental regulation as "liberal" if it was challenged by industry as too aggressive, or as "conservative" if it was challenged by an environmental group as too lax.

We used equally simple tests to code the decisions of the justices. If a member of the court voted to uphold conservative and liberal agency decisions at the same rate, we deemed him "neutral," in the sense that his voting patterns showed no political tilt. If a justice showed such a tilt, we deemed him "partisan." If a justice regularly voted in favor of agencies, we deemed him "restrained," because he proved willing to accept the decisions of another branch of government. If a justice was unusually willing to vote against agencies, we deemed him "activist," in the literal sense that he frequently used judicial power to strike down decisions of another branch.

Using this approach, they conclude the most "activist" member of the Court is Justice Scalia, and the most "restrained" is Justice Stephen Breyer. Turning to judicial ideology, they found Justice Thomas had the most "conservative" voting record (and was the most "partisan" or ideological), and Justice Stevens was the most "liberal." The least ideological, according to their methodology, was Justice Kennedy.

Miles and Sunstein note that their analysis says nothing about which hustices are "right" or "wrong." Rather, they were seeking to develop a neutral methodology for measuring one sort of judicial "activism" -- in this case rejecting the decisions of federal agencies. That said, without looking more carefully and their methodology and data set, in particular how they coded specific cases, it is difficult to evaluate their claims. (Time permitting, I'd love to dig into this, but the new baby and pending writing commitments may preclude it.) It is an interesting analysis nonetheless.