University of Chicago law professors Thomas Miles and Cass Sunstein further explain their analysis of judicial "activism" on the Supreme Court, and respond to criticisms, at the University of Chicago Faculty Blog.

The critics contend, rightly, that we do not look at the high-profile constitutional cases. But the number of such cases is small, and it isn't easy to test competing hypotheses about partisanship and restraint. Whelan argues that we fail to examine whether the agency ruling is correct. We agree that an ideal measure of judicial activism would identify the situations in which judges pursue their own ideological goals at the expense of the "correct" legal outcome. Many studies have demonstrated that ideology influences judicial decision-making in a vast range of legal contexts. But these studies generally provide no measure of the correctness of the judges' decisions. The absence of a "correctness metric" shows that it is most difficult to measure correctness in a way that can produce empirical studies of competing hypotheses.

We chose to investigate the justices' votes in challenges to administrative agencies' interpretations of law because this context provides an excellent way of testing for both partisanship and activism. The Court's own decision in the Chevron case strongly suggests that a justice's willingness to uphold an agency's interpretation of should not depend on whether the agency's decision was liberal or conservative. We think that our approach is an innovation over the existing academic literature, and we know that it is a vast improvement over unsubstantiated, anecdote-driven claims about judicial behavior.

The critics allege that the design of our study is flawed because the distinctive context of agency decisions makes it more likely that conservative judges will appear activist. If the data sets include mostly liberal decisions, then of course a liberal justice will show a higher validation rate than a conservative justice. But this objection is misconceived. In addition to measuring overall rates of agency validation for the justices, we also examined whether each justice was more likely to favor an agency when the agency decision was liberal rather than conservative. We coded the political orientation of each agency decision according to an objective method used by several prior academic studies. Agency decisions challenged by industry were deemed liberal, and those challenged by public interest groups were coded conservative. If the distribution of agency decisions were skewed in a liberal direction, as some critics allege, we should have observed few or even no challenges from public interest groups. Instead, we observed a fair number of such challenges. Moreover, our study period included many decisions from both the Clinton and the Bush administration, and it would be a big surprise if decisions by the latter were mostly "liberal."

When we looked at the data, we observed two key facts. (1) Certain justices' rates of validation -- but not others — varied widely with their own political leanings. (2) Certain justices' rates of validation -- but not others — rose when the agency interpretation agreed with their political leanings and fell when it disagreed. These two patterns suggest that certain justices are, according to this imprecise metric, reaching decisions that were likely not correct. Moreover, the patterns strongly suggest that partisanship or ideology influenced certain decisions. (Justice Thomas is the prize-winner for partisanship, but Justice Stevens is a close second.) Judicial ideology appeared to influence some justices' votes in the very context in which courts ought to defer to agencies. By our measure, these patterns smack of judicial activism.