Here’s one more study to add to the mammogram debate: New research from the f University of California at San Francisco found that mammograms often result in false positives, so much so that about half the women who get mammograms each year will receive a false-positive within 10 years of their first mammogram.

“False-positive results are common in women undergoing regular mammography and can be reduced by undergoing screening every other year rather than every year,” Dr. Karla Kerlikowske, a professor of epidemiology and biostatistics and co-author of the study, told ABCNews.com. “Women are likely to maximize their chance of benefiting from mammography and minimize the chance of harm  by undergoing mammography every other year.”

Federal guidelines currently suggest that women older than 50 receive a mammogram once every two years. But that guideline clashes with recommendations from the American College of Obstetrics and Gynecology and the American Cancer Society– both organizations recommend women begin getting annual mammograms at 40 years old.

In the study, published in the Annals of Internal Medicine, researchers examined data from nearly 330,000 women between the ages of 40 and 79 taken from a database of mammogram registries throughout the U.S. The study found that for every 10,000 women 40 to 49 years  old  who was given digital mammograms, two more cases of cancer would  be found for every 170 false-positives.

Study authors said results should help physicians make informed decisions about mammogram screenings and create personalized treatment  plans for patients.

“Targeting women age 40 to 49  … provides high-risk women in their 40s the same potential benefit as women in their 50s,” said Kerlikowske. “Targeted screening of women aged 40 to 49  years will more likely benefit those at high-risk  and not expose average and low-risk women to unnecessary harms.”