The number of hours physicians spend on the job each week is influenced by the fear of malpractice lawsuits, U.S. researchers say.

Eric Helland of Claremont McKenna College and Mark Showalter of Brigham Young University found that doctors cut back their workload by almost two hours each week when the expected liability risk increases by 10 percent.

The study, published in the Journal of Law and Economics, says the decline in hours adds up to the equivalent of one of every 35 physicians retiring without a replacement.

"The effect of malpractice risk on hours worked might seem like a small item compared to physicians moving across state borders or avoiding high-risk specialties like obstetrics," Showalter said in a statement. "However, when you aggregate that across all physicians, the total effect is quite large."

The analysis combined data gathered by insurers about medical liability risks in each state and medical specialty with physicians' responses to surveys about their workload and income.

When liability risk went up, doctors saw fewer patients each week to minimize their chance of a lawsuit. When liability risk went down, doctors saw more patients.