Just one out of every 100 U.S. doctors is responsible for 32 percent of the malpractice claims that result in payments to patients, according to a comprehensive study of 15 years' worth of cases.

And when a doctor has to pay out one claim, the chances are good that the same physician will soon be paying out on another, researchers report in the New England Journal of Medicine.

"I think people will be surprised about the extent to which the claims are concentrated within a relatively small group of practitioners. It's actually more concentrated than in earlier studies," chief author David Studdert of Stanford University in California told Reuters Health.

The result, he said, demonstrates that there are practitioners who can accumulate large numbers of claims and continue to practice.

Earlier studies looked at malpractice claims that may or may not have had merit. This study looked at all cases in the National Practitioner Data Bank where payments were made.

Those other studies typically focused on a single insurer or a single state, and repeat offenders may have been able to avoid being tracked, by moving or switching insurers, Studdert said. "We have a kind of national all-encompassing window, so we should have been able to track the doctors wherever they go."

Physicians in specialties such as anesthesiology and neurology have long been known to face an inherently higher risk for malpractice claims.

"This study rather convincingly shows, however, that even within specific specialties, malpractice claims are relatively concentrated and that a strong predictor of subsequent claims is a prior history of malpractice claims," said Dr. Anupam Jena, associate professor of healthcare policy at Harvard Medical School in Boston, who was not connected to the research.

In addition, "this is the most comprehensive exploration of the hypothesis that individual physician malpractice risk may be predictable," he told Reuters Health in an email. "To strengthen prediction, there are important factors that future analyses will hopefully consider such as patient volume, complexity of services provided, experience, and specifics on medical school, residency, and fellowship training."

Studdert's team analyzed 66,426 claims paid against 54,099 doctors from 2005 to 2014.

Nearly all were out-of-court settlements. Almost one third of the cases were sparked by a patient's death. About 1 percent of physicians had at least two paid claims against them and those doctors accounted for 32 percent of paid claims.

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One hundred twenty six doctors had more than five paid claims against them.

The median payment among all claims was nearly $205,000.

Doctors who accumulated two lawsuits where money was paid out were twice as likely to be successfully sued for malpractice a third time compared to doctors who only had one paid claim against them. Doctors with more than five paid claims were 12 times more likely to face a subsequent claim.

Compared to general practitioners, recurrence rates were roughly two times higher in the fields of obstetrics and gynecology, orthopedic surgery, plastic surgery and general surgery. The recurrence rate was highest for neurosurgeons, at 2.3 times that of GPs.

Researchers looked for other traits, beyond specialty, that might predict which doctors are more likely to have malpractice claims.

They found that physicians under age 35 were two thirds less likely to have to pay on a malpractice claim after an initial payment. The odds of paying out on a subsequent claim were 38 percent higher among male doctors than female physicians. Doctors trained outside the United States were 12 percent more likely to have to pay out on more than one claim.

If problematic physicians can be identified, it might be possible to get them into programs designed to improve their practice and help them avoid future claims.

"There's a question mark over whether interventions such as peer coaching, supervision, placing conditions on practice and so forth really are capable of returning high-risk physicians to safe practice," Studdert said. "We need to learn a lot more about these programs."