One key assumption typically shared by many assessing federal circuit court decisions is that the three-judge panels that hear cases have been randomly configured. Indeed, scores of scholarly articles have noted this 'fact,' and it has been relied on heavily by empirical researchers.
Increasingly, however, scholars are putting this widely-shared assumption (or 'fact') to data. In a 2010 JELS article, Randomness Reconsidered: Modeling Random Judicial Assignment in the U.S. Courts of Appeals, Matthew Hall (St. Louis--Poli Sci) notes critical variation across circuits when it comes to panel assignments. Similarly, and more recetly, Adam Chilton (Chicago) and Marin Levy (Duke), in Challenging the Randomness of Panel Assignment in the Federal Courts of Appeals, push back on the widely-held assumption and find: "Our results show evidence of non-randomness in the majority of the federal courts of appeals. Moreover, our findings specifically reveal a lack of randomness along several key dimensions: the distribution of conservative judges, female judges, and minority judges."
How circuit panels are configured is no longer merely an academic question. Adam Liptak, in today's New York Times, reports on a legal challenge pivoting on how the Ninth Circuit assembled its panels to hear important same-sex appeals.