Choi, Stephen J., G. Mitu Gulati, and Eric A. Posner. “Professionals or Politicians: The Uncertain Empirical Case for an Elected Rather than Appointed Judiciary,” 26 Journal of Law, Economics, and Organizations 290 (2007). (SSRN)

This empirical study analyzes the decisions of all the judges of the highest court for every state for the years 1998, 1999, and 2000, and concludes that in terms of effort, skill, and independence, appointed judges do not perform at a higher level than their elected counterparts