A follow-up to this post: Via Twitter, FiveThirtyEight’s Harry Enten has clarified for me that, rather than making his own assertion about Justice Breyer’s professional qualifications, he was using the so-called “Segal-Cover score” for Breyer. (That appeared to be the case from a chart in his post, but I wasn’t able to locate a source for the Segal-Cover score. Enten has kindly referred me to this Wikipedia page.)

To continue my “Garbage In, Garbage Out” critique of modern political science, I note that the Segal-Cover score purports to measure “perceived” (rather than actual) qualifications and that it evidently does so through the curious method (as Wikipedia summarizes it) of “analyzing pre-confirmation newspaper editorials regarding the nominations from The New York Times, Washington Post, Chicago Tribune, Los Angeles Times, St. Louis Post-Dispatch, and The Wall Street Journal.”

Thus, when Enten said that Breyer had “middling qualifications,” he meant only that some set of coders reading op-eds from these newspapers gave Breyer a cumulative rating of .545 on his “perceived” qualifications.

Insofar as the Segal-Cover score is used to help predict a nominee’s confirmability, it may well be the case that perceived qualifications matter more than actual ones. But I’m doubtful that there’s often much of a gap between the two, and I’m also doubtful that coding newspaper editorials—and trying to untangle their ideological views from their assertions about a nominee’s professional qualifications—is a very good way to measure how the Senate, or the broader public, perceives the nominee’s qualifications.