The study, which considered cases between 1980 and 2018, used a simple criterion to separate experienced lawyers from others: whether they had ever argued in the Supreme Court before. Other studies have used more elaborate definitions. A leading one, from Richard J. Lazarus, a law professor at Harvard, said expert Supreme Court litigators were those who had presented at least five arguments to the justices or who worked in offices whose lawyers had collectively argued in the court more than 10 times.

Professor Nelson said the data showed that the first argument was the key one.

“There’s just so much that goes into the first time you appear before the court in terms of nerves and the logistics of what it’s going to feel like to argue before the court,” he said. “The difference between having done that and never having done that dwarfs the difference between having done it five times versus six times.”

A 2013 study, from Jeffrey L. Fisher, a law professor at Stanford and a leading Supreme Court litigator, used the stricter definition of expertise and considered a smaller number of cases. It also found that Supreme Court specialists enjoyed a significant advantage in cases against the federal government.

The new study also considered whether lawyers had attended a leading law school as determined by U.S. News & World Report (Yale, Stanford, Harvard, the University of Chicago and Columbia) or had served as a law clerk to a Supreme Court justice.

“All else equal,” Professor Epstein said, “graduating from a top law school increases the odds of winning by almost 13 percent.”

But experience mattered, too. “There’s a 12 percentage point difference in winning for top law school graduates with experience and those without,” she said. “Put another way, for top law school grads, experience increases the odds of winning by about 38 percent over top law school graduates without experience.”

A Supreme Court clerkship was not an advantage, at least initially, Professor Nelson said.

“Former clerks are a population that you would think would be particularly likely to do very well at the court,” he said. “It’s a little puzzling that we found that’s not the case. But there’s a big difference between former clerks who have and haven’t argued before. Being a clerk and having argued before makes you a pretty potent adversary.”