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Science works in data and statistics, but medicine is made up of stories, says Elizabeth Rider, an assistant professor of pediatrics at Harvard Medical School. Narratives form the backbone of medicine — they’re the way people make sense of the evidence.

Women whose breast cancers were diagnosed with a mammogram will never be persuaded by the new mammography guidelines, Breast Cancer Action’s Brenner says. “They all say, ‘If it weren’t for that mammogram, I’d be dead right now,’” she says, “even though we know from the data that this wasn’t the case for most of them.”

“Victims of overdiagnosis don’t say, ‘Look what the system did to me.’ They say, ‘Thank God the doctor saved me,’” says Thomas B. Newman, a physician and narrative medicine expert at the University of California, San Francisco. “Nobody can say I had an unnecessary mastectomy, and nobody would want to; it doesn’t make a good story.”

Belief is a very difficult thing to overturn, especially when the belief is held by people with a vested interest in the old message. Sometimes these investments are monetary (back doctors make more money on procedures than on conservative treatment), but they can also be altruistic — breast cancer advocacy groups want to offer women something to protect themselves from a scary disease.

When the evidence presents a messy, unsatisfying picture, people are likely to take refuge in a more comforting story, even in the face of evidence that it’s wrong. It comes down to something the satirist Stephen Colbert calls “truthiness,” a term he coined in a 2005 episode of his Comedy Central show, The Colbert Report. “Truthiness is what you want the facts to be, as opposed to what the facts are,” Colbert said. “It is the truth that is felt deep down, in the gut.” The backlash against the new mammography guidelines stemmed in part from the truthiness of the message that mammography could prevent breast cancer. No matter that it wasn’t true, it was what people wanted to believe.

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