The numbers seem at odds with Liptak’s claim. Yes, Thomas has the highest shared language percentage. But it’s bizarre to say that his numbers are “unusually high,” that Thomas “relies heavily” on outside language or that “many” of his words are “not his own.” All of the Justices share language from the briefs at roughly similar rates: about 7 to 11 words out of 100. And the difference between Thomas and Sotomayor is a rounding error. It’s only 2.5 words out of 1,000. In a typical majority opinion, that’s probably the difference between including a short parenthetical quote from a precedent and leaving it out.
Liptak relies on two additional studies. These two studies looked at three Terms from over a decade ago: 2002, 2003, and 2004. Only five of the current Justices were on the Court then, so we have no idea how the Chief, Alito, Sotomayor or Kagan might measure up. They show Justice Thomas sharing language with lower court opinions and amicus briefs slightly more than other Justices. But the differences strike me as pretty modest.