Empirical studies seeking to assess the influence of ideology on judges' decisions are comparatively well-developed in the literature. Less tested, however, is the assumption that the political party of the nominating president and the relevant state senators (who share the nominating president's political party) influence federal district court judges' decisions. To get at this more narrow research question, Jonathan Nash (Emory), in Interparty Judicial Appointments (JELS, 12:4, 2015), exploits a natural experiment. As Nash explains, "[B]etween 1977 and 1998, New York was represented in the Senate by one Democrat and one Republican who had an agreement to divide appointments to the district courts in the state: the senator who shared party affiliation with the president would be allocated three of every four appointments, while the “out‐of‐party” senator would be allocated the rest." An excerpted abstract follows.
"The article employs a novel data set - consisting of all federal district judges appointed to the federal bench in New York during the time period in question, and the senator who recommended each nominee to the nominating president. If the dominant theory - that the party of the recommending senator affects judicial decision making - holds, then one would expect the theory's explanatory power to be at its apex where senators of different parties recommend judges at the same time to the same president. Yet, using median prison sentence length as a proxy for ideology in decision making, the empirical analysis finds no evidence that senatorial ideology has a statistically significant effect on district judge decision making. At the same time, it finds that, indeed, the nominating president's ideology does have a statistically significant effect. The findings are instead consistent with the minority view of lower federal court judges’ ideological leanings - that a lower federal court judge's ideology is in large part a function solely of the nominating president's ideology."