Judge Diane Wood of the U.S. Court of Appeals for the 7th Circuit should beat out federal appellate bench colleague Judge Sonia Sotomayor of the 2d Circuit for the nod as a U.S. Supreme Court candidate — at least according to an empirical view of one Chicago law school professor with a judicially prominent last name.

University of Chicago Law School Professor Eric Posner this week expanded on a 2004 study of 98 federal appellate judges in determining that Wood outranks Sotomayor in a composite rating based on quantity, quality, and independence of court opinions. Posner, who is the son of 7th Circuit Judge Richard Posner, in a posting on the Volokh Conspiracy blog, used the study’s analysis of opinions to rank Wood eighth and Sotomayor in the lower half. He included Justice Samuel Alito Jr., previously a judge on the 3d Circuit, for perspective, ranking him at No. 16 .

Posner’s father was one of two top-ranked judges in the 2004 study.

Posner was responding to the glut of speculation as to whom President Barack Obama will chose to replace Justice David Souter, who said recently that he plans to step down from the Court in June. Posner said he wanted to bring some data to the discussion on which of the two judges, both of whom have been widely cited as likely candidates, would be most qualified, though he noted his own bias in that Wood also teaches at the University of Chicago.

“I just want to get people to think about how they can use this publicly available information in a systematic, objective way,” Posner said in an interview. “Just focusing on the data confirmed the very high reputation [Wood] has around here.”

The 2004 study by G. Mitu Gulati and Stephen J. Choi, entitled “Choosing the Next Supreme Court Justice: An Empirical Ranking of Judge Performance” and published in the Southern California Law Review, uses the number of opinions written by 98 federal circuit court judges from the beginning of 1998 through 2000, the number of times their top opinions are cited by other judges, and the extent to which they dissent or write a majority opinion from which others dissent to rank the judges by score. While the study didn’t include Sotomayor because of her appointment in October 1998, Posner added an analysis of her opinions by gathering the same data for her from the start of 1999 through 2001 and from 2006 alone to offset for a “freshman effect,” he said.

“That’s a data point [on Sotomayor], but it’s not really enough to come to a conclusion on whether she should be a Supreme Court justice,” Posner said.