Source: Allison P. Harris, Maya Sen, Annual Review of Political Science, Vol. 22, 2019
From the abstract:
How do we know whether judges of different backgrounds are biased? We review the substantial political science literature on judicial decision making, paying close attention to how judges’ demographics and ideology can influence or structure their decision making. As the research demonstrates, characteristics such as race, ethnicity, and gender can sometimes predict judicial decision making in limited kinds of cases; however, the literature also suggests that these characteristics are far less important in shaping or predicting outcomes than is ideology (or partisanship), which in turn correlates closely with gender, race, and ethnicity. This leads us to conclude that assuming judges of different backgrounds are biased because they rule differently is questionable. Given that the application of the law rarely provides one objectively correct answer, it is no surprise that judges’ decisions vary according to their personal backgrounds and, more importantly, according to their ideology.