It's not often that a football game can teach us something useful about mammography. But look what happened on Sunday after New England Patriots coach Bill Belichick decided to go for a short fourth-down conversion from his own 28 yard line, with a late six-point lead. The Colts stopped the Pats cold to take possession, and star quarterback Peyton Manning quickly fired off a touchdown pass to win the game for Indianapolis.
Like a woman considering whether to have a mammogram, Belichick—widely considered one of the wiliest and most data-driven coaches in the game—had to process complex probabilities to make a decisive, if controversial, call. What's amazing is how mathematically sophisticated fans and sports commentators are in their analysis of Belichick's decision not to punt. Sports Illustrated labeled Belichick's call "I'm-smarter-than-they-are hubris," but only after it reviewed the preceding plays in numerical detail. On the other side, using a complex mathematic model, two fans gave Belichick a "thumbs up" for a "courageous and correct call": They calculated the Patriots' chances of winning at roughly 77 percent by going for it and 76 percent if they had punted instead. The New York Times football blog and the New Republic also dissected probability equations on the matter.
Journalists and physicians explaining the U.S. Public Health Service's widely publicized change in mammogram recommendations—it now suggests most women start receiving them every other year at 50, instead of 40—might take a page from the sports commentators' playbook. If the sports media have no problem filling newspapers and the airwaves with complex statistics—and often discussing them clearly—why do the health media treat the same consumers like innumerate dolts, especially when women's lives are at stake? Hopefully it's not because they think only testosterone-drenched sports fans can handle the math.
Even though they use the same data, the American Cancer Society, U.S. Public Health Service, and National Cancer Institute—not to mention Canadian and British health authorities—now fail to agree on when women should start getting mammograms. Some say at 40, others at 50. That's why it's critical to separate each organization's opinions from the facts. Encouragingly, there's really no disagreement about the latter.
Here's the bottom line about mammography: Getting screened or not screened for breast cancer is a gamble. There is no right answer, but there is helpful statistical guidance. There are two broad ways to handle mammography for women under 50 years old: to treat them as homogenous and statistically naive (the cookie-cutter approach, usually favored by policymakers) or to assume greater patient savvy (the personalized approach, increasingly favored by clinicians and patients).
Let's first review the "cookie cutter" approach the way a sports analyst might. For the average woman turning 40, there is a 1.4 percent—about one in 100—chance of getting invasive breast cancer before the age of 50. In baseball terms, she bats .986 against breast cancer. (For comparison, a woman turning 50 has a 2.4 percent chance of breast cancer over a decade; she bats .976.) Further, most cancers are treated successfully, no matter how they're found, so survival rates are even more favorable.
How does mammography improve these stats? Researchers generally agree that mammograms save lives, but—this is critical—catching breast cancer early changes the outcome in only 15 percent of cases. So consider the actual numbers: For the average 40-year-old woman, annual mammography for a decade increases one's overall chance of breast cancer survival from roughly 99.7 percent to 99.8 percent. That is, it increases the final batting average by only 0.001. According to the National Cancer Institute, there's also a downside. During this time, half of all screened women will have at least one suspicious mammogram, and one-quarter of them will end up getting a biopsy. Mammograms in women from 40 to 50 years old cause a huge number of false positives, resulting in about 100 biopsies for every life saved. Even more worrisome: It's possible the radiation from those mammograms may end up causing more cancers than they prevent.
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