Many of the lawsuits analyzed contained no evidence that a medical error was committed or that the patient suffered any injury, the researchers reported.
The vast majority of those dubious cases were dismissed with no payout to the patient. However, groundless lawsuits still accounted for 15 percent of the money paid out in settlements or verdicts.
The study's lead researcher, David Studdert of the Harvard School of Public Health, said the findings challenge the view among tort reform supporters that the legal system is riddled with frivolous claims that lead to exorbitant payouts.
"We found the system did reasonably well in sorting the good claims from the bad ones, but there were problems," he said.
However, the American Medical Association, which favors caps on malpractice awards, called the study proof that a substantial number of meritless claims continue to slip through the cracks, "clogging the courts" and forcing doctors to waste time defending them, association board member Dr. Cecil Wilson said in a statement.
The findings were published in Thursday's New England Journal of Medicine.
The study found 3 percent of claims analyzed were filed by patients who had no injury. Of the claims that involved injuries, two-thirds were caused by medical error. But the remaining injury claims, or 37 percent, lacked evidence of a medical mistake, and most of those — 72 percent — were thrown out or otherwise resolved without a payout to the patient.