Medical errors don't just happen at the hospital, according to a new study that highlights safety problems in the doctor's office as well.

Researchers found that about half of U.S. malpractice payments—a proxy for medical errors—from 2009 involved patients seen outside of the hospital.

Previous studies have focused mostly on the situation inside hospitals, some of which now have checklists and other systems in place to help prevent devastating mistakes.

But "invasive and high-technology diagnostic and therapeutic procedures are increasingly being performed in the outpatient setting," the researchers note, so they decided to compare the number and seriousness of adverse events in inpatient and outpatient settings, as reflected by malpractice claims.

A 1999 report from the Institute of Medicine suggested as many as 98,000 Americans die from preventable medical errors every year, costing society billions of dollars, and consumer advocates say little has changed since then.

That the number of malpractice claims would be virtually the same for hospitals and doctors' offices was unexpected, Dr. Tara Bishop, who worked on the study, told Reuters Health.

"We were actually very surprised by that finding," Bishop, of Weill Cornell Medical College in New York, said. "I hope it's a wake-up call for the medical community and for patients, so we can start working on ways to solve these problems."

The researchers analyzed malpractice claim payments from the National Practitioner Data Bank from 2005 to 2009. Overall, the number of payments dropped slightly for patients treated both inside and outside of the hospital.

In 2009, the last year of the study, there were 4,910 payments due to inpatient errors, 4,448 due to outpatient errors, and 966 involving both settings. Together, these payments were worth more than $3.3 billion.

"These weren't trivial errors—death and major injuries were the most common reason for malpractice claims," said Bishop. "It's nice to see this trend coming down, but we still don't know if it's due to better patient safety."

According to the new report, published in the Journal of the American Medical Association, there are 30 times as many outpatient visits as hospital discharges every year.

Bishop said the most common errors were different across the two settings, with surgical mistakes dominating the claims for hospitalized patients and misdiagnosis being the biggest problem at the doctor's office.

That means fixing the problems outside hospitals will take separate efforts, such as training doctors to communicate better with patients.

In a related editorial, Dr. Gianna Zuccotti and Dr. Luke Sato of the Harvard Medical Institutions in Boston say malpractice claims represent only the tip of the iceberg for medical errors.

They note that the decrease in claim payments over the study period—by more than 2,500—is good news.

The bad news, they add, is that rigorous, effective programs for controlling the risk of errors outside the hospital don't exist right now.

According to Bishop, patients can also help lower the chance that their doctor will make a mistake by learning about the tests and medications they get, and keeping their doctor up to speed about what's happened between visits.

"I do hope that patients will realize that it's important to take control of what happens in their healthcare," Bishop said.