The vast majority of cases do settle  from 80 to 92 percent by some estimates, Mr. Kiser said  and there is no way to know whether either side in those cases could have done better at trial. But the findings, based on a study of 2,054 cases that went to trial from 2002 to 2005, raise provocative questions about how lawyers and clients make decisions, the quality of legal advice and lawyers’ motives.

Critics of the profession have long argued that lawyers have an incentive to try to collect fees that are contingent on winning in court or simply to bill for all the hours required to prepare and go to trial.

“What I would want them to look at was whether or not the lawyers had a strong financial incentive to go to trial,” said Cristina C. Arguedas, a criminal defense lawyer in Berkeley, Calif., when told of the study. “I’m not suggesting the answer, because I don’t know, but that would be my question.”

The study, which is to be published in the September issue of the Journal of Empirical Legal Studies, does not directly answer Ms. Arguedas, but it does find that the mistakes were made more often in cases in which lawyers are typically paid a share of whatever is won at trial.

On average, getting it wrong cost plaintiffs at about $43,000; the total could be more because information on legal costs was not available in every case. For defendants, who were less often wrong about going to trial, the cost was much greater: $1.1 million.