Universal Mammograms Show We Don’t Understand Risk

The following originally appeared at The Upshot (copyright 2014, The New York Times Company).

In an effort to reduce childhood injuries, the American Academy of Pediatrics issued a policy statement in 2001 recommending that all kids younger than 2 sit in safety seats in airplanes as they do in cars.

The change meant that families traveling with small children would no longer be able to have them sit on an adult’s lap. Instead, parents would need to buy an extra ticket. But the added expense of purchasing a seat for small children would be prohibitive for some traveling families. They might choose to drive instead, which is a real problem, because driving is far more unsafe than flying.

It turned out that if just 5 percent of families chose to make an additional 400-mile road trip because of this policy, then the number of children killed each year would increase. The policy would also be enormously expensive.

Try relating this story to people, and you quickly learn that instinct often trumps data. They just know, deep in their hearts, that flying is scary and dangerous. They just believe that driving is safer. Convincing them otherwise is nearly impossible.

People are often terrible at understanding risk. These misunderstandings make creating health policy much more difficult. They also make reducing health care spending very hard.

Recently, a manuscript in the New England Journal of Medicine described the disconnect between women’s beliefs about their risks from breast cancer and the actual risks. Out of any group of 1,000 50-year-old women today, about five are likely to die of breast cancer in the next 10 years. If all 1,000 women received mammograms at age 50 and every two years for the next decade, though, the number of deaths might decline by only one — to four, the collected research shows.

But if you ask women about the risks of breast cancer and the benefits of universal screening, as researchers did in a study, the answers are very different. On average, respondents said that more than 160 out of every 1,000 would die without screening. With screening, the number of deaths would drop in half, to about 80.

Even without a universal screening mammogram program, the actual likelihood of a 50-year-old woman dying of breast cancer in the next 10 years is one half of one percent. And adding a screening program has only a marginal effect on that risk. Diagnostic methods these days catch most cases of breast cancer that can be effectively treated, and much of what is picked up by universal screening is over-diagnosis.

Men, of course, suffer from these same biases. I could easily have substituted the above story with one on prostate-cancer screening, and the gist would be the same.

Whenever I discuss data like these, I am inundated with angry emails telling me that mammograms or prostate-cancer screening saved a loved one’s life. Or I’m presented by outright denials that the data I’m describing are true. People just know that breast cancer and prostate cancer will kill people, and that screening will save them.

Why is all of this important? Because we have a limited amount of money to spend on health care each year. Money we spend on things that don’t work is money we can’t spend on things that do. The Affordable Care Act has, within it, language that specifically “protects” mammogram coverage. Screening must be paid for, even if we find that universal screening doesn’t work or results in harm.

Screening programs are expensive. Screening mammograms probably cost us more than $7.8 billion a year, which is equal to more than 25 percent of the National Institutes of Health budget for research. The true cost of screening is even higher, because it leads to over-diagnosis of breast cancer, and treatments that don’t improve health.

Even if you believe, as many do, that the United States spends too little on women’s health, and that taking money away from breast cancer is wrong, wouldn’t this money be better spent paying for treatment of confirmed cases, for research into new drugs, or even for support for women who are undergoing treatment? Wouldn’t those steps improve the lives of more women than universal screening?

We can’t make these kinds of changes, though, while we allow beliefs to trump facts. Study after study, and our reaction to them, show that our perceptions don’t line up with reality. If we want to live longer, healthier, and, most importantly, better lives, it’s worth fighting some of those assumptions.


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