Problem is, some women may think they should now skip their mammograms.
First consider the evidence.
The Canadian study is sound, judging from a careful reading of the report in the British Medical Journal (See the link below to download).
For example, women were chosen using scientific methods, including random selection, and were picked “blind,” meaning; researchers didn’t know which women were placed in the mammography and no-mammography groups.
About 90,000 women were followed (the number tapered off somewhat throughout the 25-year timeframe)—and that’s a lot for any study, which usually relies on much smaller samples. Plus, a larger study gives researchers more confidence in the accuracy of their results.
The Canadian researchers found no significant differences in cancer deaths among women after following them for as long as 25 years.
They found 1005 women in the study died from breast cancer and the numbers were similar for the mammography group (500 women) and the non-mammography group (505 women).
So, the report that’s been making headlines notes no statistically significant difference among breast cancer deaths for women who had a mammogram or skipped a mammogram from 1980-1985.
That’s a pretty robust finding.
Bear in mind, however, the study followed women ages 40 to 59 in the 1980s.
What we don’t know is how this information applies to you and me.
And that’s where this study becomes a teaching moment for those of us who study science communication and teach classes in research methods.
If you think this study applies to you, then you’ve made a mistake called the ecological fallacy.
It happens all the time and you’re not alone.
We hear about a study where folks live longer who drink Greek coffee or we read fluoridated water harms children.
And then we think those results apply to us. And that’s the fallacy.
We can’t assume the Canadian study applies to you and me.
It’s a pity that some women will skip testing after seeing a TV news report or reading a headline that questions mammograms.
A New York Times reader fell headlong into the fallacy and says she was “vindicated” by the Canadian study.
The reader refuses to get a mammogram and the study reinforces her beliefs.
But, as humans, we constantly look for evidence that supports our pre-existing beliefs.
Me? I’m an espresso drinker so I cherish studies that show coffee enriches my life. But when I read a study that says I should ditch the ice cream in favor of celery sticks I reckon the study is flawed.
Recriminations aside, we’re better off when we approach studies like scientists: be critical, be objective, read the original study rather than the news report alone–and don’t take it personally if the evidence doesn’t support your beliefs.
Review the evidence in the context of the whole body of information about mammograms and their risks and benefits.
The Times reader who felt vindicated and refused mammograms may be at low risk for breast cancer. She might be able to skip mammograms without harm.
But the results of the Canadian study don’t necessarily apply to her individual case.
[Botticelli’s Venus de Milo rendering, copyright free]
Read Gina Kolata’s story about the Canadian study in the New York Times http://www.nytimes.com/2014/02/12/health/study-adds-new-doubts-about-value-of-mammograms.html?_r=0
Read the original study http://www.bmj.com/content/348/bmj.g366