About a quarter of Americans have used websites that rate physicians, and although some people said the sites helped them pick a doctor, others said they distrust the ratings, according to a new study.

Researchers surveyed more than 2,000 U.S. adults in 2012 about their knowledge and use of online physician ratings sites. The survey did not mention any sites specifically, but popular ones include healthgrades.com, ratemds.com and vitals.com.

About 65 percent of respondents said they were aware that such ratings sites existed. In contrast, about 87 percent said they were aware of online ratings for cars, and 81 percent said they were aware of online ratings for restaurants.

Overall, 23 percent of respondents said they'd used such ratings sites in the past year. Of those who did use the sites, 35 percent said they'd picked a doctor based on good ratings, and 37 percent said they'd avoided certain doctors because of bad ratings. [7 Medical Myths Even Doctors Believe]

Of those who did not use online physician ratings, 43 percent said they did not trust the information.

Nineteen percent of participants considered physician's ratings on websites to be "very important" when selecting a primary care doctor, compared with 46 percent who they considered a doctor's years of experience to be very important, and 89 percent who said they considered whether a doctor accepts their health insurance to be very important.

"Clearly some people don't trust the sites. But at the same time, we found a substantial percentage who had not only visited the sites but used them to make decisions," said study researcher Dr. David Hanauer, an associate professor in the Department of Pediatrics at the University of Michigan Medical School.

"Consumers are used to looking up ratings, so it is not surprising that they would turn to this familiar online medium to also seek physician ratings," Hanauer said.

Still, there's been little research into whether the information on these sites is valid, and at least one study found that doctors sometimes write the ratings themselves.

"My personal opinion is that it is difficult to trust the sites partly because of a lack of transparency about who is leaving the ratings," Hanauer told Live Science. "It's a difficult problem to solve because some people might not want to leave ratings or comments if their identity were disclosed, but at the same time, anonymous feedback leaves sites open to misuse and abuse. Even if the ratings are all true, the small number of ratings for many physicians raises questions about how representative they are."

A better way to provide online physician reviews to the public may be needed, despite the fact that doctors are generally resistant to the idea, Hanauer said.

"The use of the sites does not seem to be decreasing, and therefore it might be time to come up with better approaches to provide what the public is looking for in a more open, transparent and trustworthy manner," Hanauer said.

The researchers noted that the new study analyzed a sample of participants that was representative of the United States, but because the survey was Internet-based, the respondents may have been more Web-savvy than the average health care consumer.

The study was published in the Feb. 19 issue of the Journal of the American Medical Association.

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This story was originally written for LiveScience and has been republished with permission here. Copyright 2014 LiveScience, a TechMediaNetwork company.