Thank you, this was a careful and interesting study. This is the conclusion I draw from it: Some of 70 judges examined in Cook County, Illinois, showed statistically significant variation in incarceration rates, although not in sentence lengths, for non-drug crimes, but not drug crimes, and this variation was associated with race, or some factor that correlates with race, and it is not clear if the variation favors whites over African American defendants, the reverse, or a mixture of both. Section 2, "Literature Review," gives an overview of the "great deal of scholarship investigating the role of race in the courtroom" and describes many problems in earlier studies. Section 6, "Potential Confounding Factors and Analysis by Crime Category," recognizes that differential judicial treatment could be explained by factors that correlate with race. Other factors not considered (the application of DNA testing is mentioned) "could in principle generate the type of variation we observe if these unobserved features vary systematically across racial groups and judges differ in their treatment of these characteristics." I wonder if education level could be such a factor. If defendants of one race more often appear uneducated, a biased judge might be inclined to "teach them a lesson," whereas a more articulate defendant simply "made a mistake." With enough data, it would be possible to test for these factors. This study examined over 600,000 felony cases, but after applying strict rules on what cases would provide good evidence, only 34,227 cases remained. When these are considered separately by type of crime, "each category contains a relatively small number of observations. In performing this analysis (data not shown), we find no evidence for excess heterogeneity in racial gap in any crime category. This result is almost certainly due to a lack of power." The authors, following the important rule that you must not fool yourself, required a high standard of evidence, and the conclusions they were able to justify are correspondingly weak. Race, or something that correlates with race, makes a difference to some judges in some cases. As usual, more research is advised. I imagined that sentencing disparity would be an obvious place to look for evidence of racism, but in my view this evidence is not very persuasive. Do you have any suggestions as to where else we might look?African Americans may commit different crimes than whites, and judges may have different sentencing policies for different crimes. For example, suppose that some judges are stricter on sentencing for violent crimes than they are for other crimes. Suppose also that African Americans commit more violent crimes. This correlation would then lead to the appearance of heterogeneity in racial gaps in sentencing even if judges were race blind.
While these confounding factors are still potentially a concern, the approach in this paper advances the field in light of previous work, because now the unobservable case characteristics would have to be correlated with the defendant’s race and elicit differential treatment across judges.
As an aside, b_b, the link you sent me is a good example of the importance of the lesson that "you must not fool yourself—and you are the easiest person to fool." I didn't read the article until now, and I see it both amplifies the conclusions of the study and diminishes the reservations. The researchers have "demonstrated conclusively" that "racial bias affects judicial sentencing;" they "offer statistical proof" that judges vary in their treatment of race. When the researchers say "We find evidence ... providing support for the model ..." the copywriter translates this to "race is affecting sentencing decisions" in the same paragraph. Most egregiously, "the technique eliminates the problem of 'unobserved variables,'" which the researchers took pains to point out as a problem with their study. Many people will read the press release and not look closely at the study. It's always a good idea to cut out the middleman!
Interestingly, the data only say that racial bias exists, but not whom it is working against (or for). However, we do have evidence that black people were targeted for sentencing disparity in mandatory minimum sentencing laws. The Supreme Court has ruled against these laws (specifically harsher sentences for crack than powder cocaine), but I don't think we're completely rid of them.