A related difficulty with many of the early studies of gender and judging involves distortions in the sample. On the federal bench, women skew to the political left, while men are more evenly distributed. This makes it problematic to use simple models of statistical analysis and samples of limited size. If, for example, researchers are looking at federal sex-discrimination cases during a particular period, there may be too few conservative women to know whether their presence on a panel would have had the same effect as that of a more liberal female judge. Boyd, Epstein, and Martin avoid this problem by matching pairs of federal employment-discrimination cases that are similar in relevant respects except for the sex of one member of the panel. Their study, the best one to date, finds that the probability of a judge ruling in favor of a discrimination plaintiff decreases by about 10 percent when the judge is a man. When a woman is on the panel, the likelihood that a male colleague will rule in favor of the plaintiff increases 12 percent to 16 percent.
This finding is consistent with two commonly cited earlier studies. One, from the 2005 Yale Law Journal, concluded that women on the appellate bench were significantly likelier than their male colleagues to perceive conduct as sexual harassment or discrimination, even when controlling for ideology and other background factors. Moreover, the presence of a woman on an appellate panel more than doubled the likelihood that a male judge would rule for the plaintiff in a sex harassment case, and tripled that likelihood for a sex-discrimination claim. A similar 1993 study in Judicature, which Sotomayor invoked in her speech, found that women on the federal appeals court, whether Democrats or Republicans, were more likely than their male colleagues to vote for plaintiffs in employment-discrimination cases.
Yet even if such research cumulatively suggests that the sex of a judge does influence the outcome of certain cases, sex is by no means a reliable predictor of the voting behavior of any particular nominee. Much depends on other aspects of a judge's background and how they influence his or her world view. Consider Justices Thurgood Marshall and Clarence Thomas. One of Marshall's greatest contributions to the court was his firsthand experience of racial injustice. As his colleague Justice Byron White recalled, Marshall "would tell us things that we knew but would rather forget; and he told us much that we did not know due to the limitations of our own experiences." Clarence Thomas, too, experienced poverty and racism as a child, but he does not draw the same lessons from them. For similar reasons, simply putting another woman on the court would not necessarily be good for a feminist legal agenda. It matters greatly which woman.
In short, the importance of diversity in judicial appointments should be neither overlooked nor overstated. Equally important are the other qualities that Obama mentioned as criteria for his selection: a "sharp and independent mind," a record of "excellence and integrity," and a capacity for "empathy." Concern for all of those qualities should guide the confirmation process.
This article also appears in Double X.