Criminal law and sentencing wonks will want to see Reviewing the Sentencing Guidelines: Judicial Politics, Empirical Evidence, and Reform, by Max Schanzenbach (Northwestern) and Emerson Tiller (Northwestern). The study matches offenders to the sentencing judge and controls for political party of the judge's appointing president and crime type. An excerpted abstract follows:
"We confirm the widely-held belief that political ideology matters in criminal sentencing – specifically, Republican-appointed judges give longer sentences than Democrat-appointees with regard to certain crimes. More interestingly, we find evidence consistent with positive political theory that such decision making is nested within the broader political-ideological relationship of the sentencing judge and the overseeing circuit court."