If doctors don’t understand health statistics, how can they possibly properly counsel patients? 

“In these mammography wars, rational thinking can be easily lost.” Mammograms are big business, bringing in about seven billion dollars a year, but it would be a bit too “cynical to believe that the pushback from mammogram critics “stems only from self-interest of radiologists, surgeons, managers, and so on, whose daily bread depends on the continuation of mammographic screening programmes.” It just makes intuitive sense that mammograms should work, but that’s why we have science—so we can put things to the test. “We owe it to [our patients] to be ‘evidence-based’ rather than ‘faith-based.’” They deserve an objective analysis of the data. 

“We have done a dismal job of accurately informing the public about screening.” Why? One reason is that the doctors themselves aren’t informed, as I discuss in my video Why Patients Aren’t Informed About Mammograms. A survey of radiologists found that 96 percent overestimated a middle-aged woman’s risk of breast cancer, for example. In one sneaky study, researchers “contacted gynecologists’ practices and made an appointment for telephone counseling.” During the actual phone consultation, they pretended to be a concerned family member, asking about the benefits and harms of mammograms. “Although all gynecologists appeared motivated and concerned with sufficiently answering our questions, they lacked information as well as knowledge of how to communicate information on medical risk.” 

In an article titled “When Doctors Meet Numbers,” the authors write that “we cannot take for granted the ability of physicians to understand and interpret quantitative information and to use it to the best advantage of the patient.” In fact, this is “an educational blind spot” for physicians that was identified more than 80 years ago. In one study, for example, 151 practicing physicians were asked a series of multiple choice and true-or-false questions to gauge their practical understanding of some key concepts. They failed miserably, getting just 55 percent correct, which is only about 20 percent more than they would have gotten right just by guessing randomly.

If doctors don’t understand health statistics, how can they possibly counsel patients properly? In a famous study, one hundred physicians were asked what the chances were of a woman actually having breast cancer if her mammogram came back positive. They were given all the numerical data so they could do the math, but 95 out of 100 not only answered incorrectly, but they were spectacularly wrong—as in off by 1000 percent.

Even doctors at Harvard had a problem. Faculty, staff, and students at Harvard Medical School were asked a simple question, and 82 percent got it wrong. That was a few decades ago, though. What happened in an updated survey in Boston? Only 77 percent got it wrong, but they were off by an average of about 3000 percent, demonstrating medicine’s continued “uncomfortable relationship with math.”

“Only 12% of the 4713 surveyed obstetrics-gynecology residents were able to correctly answer 2 simple questions on medical statistics…What will the uninformed 88% of these residents say when their first patient asks about her chance of truly having breast cancer given a positive mammogram?” What’s particularly frightening is that, in some studies, those doctors “most confident in their estimates were furthest away from the correct response.” They didn’t even know that they didn’t know. “All of these studies document the same phenomenon: A considerable number of physicians are statistically illiterate, that is, they do not understand the statistics of their own discipline.” 

So, when physicians say they don’t have time to fully inform patients about the benefits and harms of a test, maybe that’s a good thing if they don’t even know what they’re talking about. Instead, they may just talk about the benefits of breast cancer screening and skip “any discussion of adverse effects.” Given all of this, we shouldn’t be surprised when nine out of ten women “believed that this screening could not harm a woman without breast cancer,” while often greatly overestimating the benefits. “In fact, the benefits and harms are so evenly balanced” that perhaps we should just inform women and let them make up their own minds. That’s not what you hear from advertising campaigns, though. An ad “simply tells women to be screened, overstates the benefit of mammography, and ignores harms altogether.” Indeed, instead of education, an “obvious approach was to use powerful tools of persuasion—including fear, guilt, and a sense of personal responsibility—to convince people to get screened.” Whatever it takes. 

It’s “easy to ‘sell screening: just magnify the benefit, minimize the cost, and keep the numbers less than transparent.” To put routine screenings to the test, studies have randomized hundreds of thousands of women to get mammograms or not, but what’s the point if we’re not going to share the results? “We spend billions on clinical studies but fail to ensure that patients and physicians are communicated the results transparently.” Maybe women should “tear up the pink ribbons and campaign for honest information.” How else can women make informed decisions? Instead, hospitals throw “monthly ‘mingle and mammograms’ parties.” In addition to “appetizers, foot massages, and bags emblazoned with the logo ‘fight like a girl,’” maybe they should “serve[ ] women balanced information about the benefits and harms of screening to chew on.

Unfortunately, many doctors display a similar ignorance about nutrition. See, for example, Physicians May Be Missing Their Most Important Tool.


Mammography screening brings in about seven billion dollars a year, and the industry suffers from conflicts of interest amongst radiologist, surgeons, and others who may profit off of the procedure.
One reason the medical community has failed to accurately inform the public about screening is that physicians themselves aren’t informed. A survey of radiologists found that 96 percent overestimated a middle-aged woman’s break cancer risk, for example.
An “educational blind spot” for doctors was identified more than eight decades ago—namely, physicians may not understand and interpret quantitative data, nor be able to use the information to the patient’s advantage.
In a famous study, a hundred physicians were asked what a woman’s chance of having breast cancer would be with a positive mammogram result, and 95 out of the 100 doctors not only answered incorrectly, but were off by 1,000 percent.
Study after study, including those with physicians at the esteemed Harvard University, show a significant number of doctors are “statistically illiterate, that is, they do not understand the statistics of their own discipline.”
It follows that, instead of fully informing patients about the benefits and harms of a screening test, physicians may omit discussion of risks and only present the benefits. As such, it is understandable that nine out of ten women believe mammograms could not be harmful to a woman without breast cancer.
The benefits and harms of mammograms, however, are evenly balanced.
Women deserve to know the benefits and harms of screening to make informed decisions about whether the risk is worth it.

There is so much confusion when it comes to mammography, combined with the corrupting commercial interests of a billion-dollar industry. As with any important health decision, everyone should be fully informed of the risks and benefits, and make up their own mind about their own bodies. This is one installment in my 14-part series on mammograms, which includes: 

Nine out of Ten Women Misinformed About Mammograms
Mammogram Recommendations: Why the Conflicting Guidelines?
Flashback Friday: Should Women Get Mammograms Starting at Age 40?
Do Mammograms Save Lives?
Consequences of False-Positive Mammogram Results
Do Mammograms Hurt?
Can Mammogram Radiation Cause Breast Cancer?
Understanding the Mammogram Paradox
Overtreatment of Stage 0 Breast Cancer DCIS
Women Deserve to Know the Truth About Mammograms
Breast Cancer and the Five-Year Survival Rate Myth
Why Mammograms Don’t Appear to Save Lives
Why Patients Aren’t Informed About Mammograms
The Pros and Cons of Mammograms

For more on breast cancer, see my videos Oxidized Cholesterol 27HC May Explain Three Breast Cancer MysteriesEggs and Breast Cancer and Flashback Friday: Can Flax Seeds Help Prevent Breast Cancer?

I was able to cover colon cancer screening in just one video. If you missed it, see Should We All Get Colonoscopies Starting at Age 50?.

Also on the topic of medical screenings, check out Flashback Friday: Worth Getting an Annual Health Check-Up and Physical Exam?Is It Worth Getting Annual Health Check-Ups? and Is It Worth Getting an Annual Physical Exam?

In health,

Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live presentations:

2019: Evidence-Based Weight Loss

2016: How Not To Die: The Role of Diet in Preventing, Arresting, and Reversing Our Top 15 Killers

2015: Food as Medicine: Preventing and Treating the Most Dreaded Diseases with Diet

2014: From Table to Able: Combating Disabling Diseases with Food

2013: More Than an Apple a Day

2012: Uprooting the Leading Causes of Death