Their report followed another earlier this month by a coalition of consumer organizations that led regulators in some states to challenge medical malpractice insurance rates.

"The change in medical malpractice loss costs over the past ten years shows the same pattern as paid losses, year after year rising near the level of medical inflation," said J. Robert Hunter, director of insurance for the Consumer Federation of America.

He said there was "no justification for the sudden spike in rates that American physicians have endured, other than the lack of competition that occurs during the insurance industry's periodic hard market episodes."

David Corum, American Insurance Association assistant vice president, questioned the methods used by the Center for Justice and Democracy, parent of AIR.

"For example, CJD examines the overall loss costs for all types of individual medical providers, not just those limited specialties targeted by the lawsuit industry," Mr. Corum said.

The AIR study also found that limits on awards and other litigation rules changes have not affected costs. "Between 2000 and 2004, states with fewer limits on tort law saw an average annual increase in medical malpractice loss costs of 3.8 percent, while those with more limits saw a slightly larger average increase of 4.8 percent," Mr. Hunter said.