In all, they find that 10 percent of women who start having mammograms before age 40 have a relatively high positive test rate of 0.84 percent, possibly because they experience symptoms. By contrast, only 0.56 percent of the women who start getting mammograms at age 40 test positive for breast cancer, and the number of late-stage cases among them falls by 6 percentage points compared to people who get screened before age 40.
They also considered a third group -- women who don't get mammograms even when they are recommended above age 40. Compared to this group, women who do start screenings in the 40s (whom the researchers call "compliers"), are also more likely to get other forms of preventative care, including flu shots and cervical cancer screenings, and have fewer emergency room visits for any reason. It is harder to assess the incidence of cancer for the women who do not get mammograms even when they are recommended at age 40. But the clinicians' model enables the researchers to estimate that the cancer risk among these unscreened women is likely higher than it is among the compliers.
"This is a great example of how health economics can build off medical research, and vice versa," Oostrom says.
Overall, Finkelstein says, "When you make age-based recommendations, it looks like the people who are most likely to follow them are the ones for whom it's least beneficial -- which doesn't mean it's not beneficial, but those are not the people you most want to target."
Better ways to target?
The scholars also suggest that their findings highlight the value of recent proposals by clinical researchers to target recommended screenings to higher-risk groups -- potentially based on factors like the age of mothers at first birth, or genetic markers -- instead of, or together with, age-based guidance. To be sure, they recognize that such methods would still require additional medical research.
More immediately, the researchers say, they would like the findings to become part of the ongoing policy discussion.
"We want to think about choice and behavior," Finkelstein says, noting that the ways people use health care, if studied carefully, can be applied to develop robust new policies.
The researchers also hope the paper will encourage further studies of the same main issue across a range of diseases. Earlier this fall, the U.S. Preventive Services Task Force changed its recommended start age for colorectal cancer screening from 50 to 45.
"We studied mammograms, but there are other kinds of cancer screening that are also very important," Ostriker says. "This concept that the average person is not necessarily the same as the person who elects to participate is, I think, very pervasive. And getting more attention for that is hopefully going to be helpful."
Support for the research was provided, in part, by the Laura and John Arnold Foundation, the National Institute on Aging, and the National Science Foundation.
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