Mental Mishaps

Errors in perceiving, remembering, and thinking.

by Ira Hyman

Breast Cancer Screening Advice that Doesn't Make Sense

Breast Cancer Screening Advice that Makes No Sense

Published on December 14, 2009 by Ira Hyman in Mental Mishaps

A few years ago, my family lost a friend who died from breast cancer at far too young an age. I also know someone who had breast cancer at a young age, but who has thrived with appropriate treatment. Why does one person die and another live? Whenever I think of these two friends, I wonder if the first woman could have been saved if her cancer had been caught sooner.

The timing of breast cancer screenings is currently under re-evaluation. The United States Preventive Services Task Force has recommended waiting until age 50, rather than 40, for most women to begin regular mammograms. The Task Force has also advised that doctors should stop teaching women to conduct personal breast exams. Many people find the new screening recommendations hard to accept. These recommendations disagree with our intuitions concerning the value of mammograms and personal exams. There are at least two cognitive reasons why people have found these new guidelines difficult to accept.

First is the availability heuristic. When faced with an opportunity to evaluate something, such as the value of cancer screenings, we are often confronted with a variety of evidence that we could use. One type of evidence is statistical information. This is what the Preventive Services Task Force has offered. Frankly, many people don't like stats. People are not experts in computing the probability that a screening test will provide accurate results. Instead, Daniel Kahneman and Amos Tversky argued that people reason about complex situations by using whatever information comes to mind easily - that is, the information that is quickly available. What comes to mind when we think about breast cancer? We think about the people we've known who have fought breast cancer. Maybe we know someone whose cancer was caught early because of the screenings that the US Preventive Services Task Force has recommended cutting. Maybe we know someone who died and we wonder if she could have been saved if she had received a mammogram sooner. We probably don't know, or at least have a hard time remembering, women who have had false positive screening tests. Maybe they've never talked with us about the emotional and other difficulties they faced because of an incorrect reading on a mammogram. The availability heuristic predicts that we reason from the things that come to mind easily. Thus we think that these screenings seem so valuable for the women we've known.

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The second cognitive issue with the new guidelines is the problem of framing. Many researchers have found that how a situation is presented affects how people make their evaluations. Of course, this is obvious, but there is a particularly important aspect of framing for breast cancer screening. People like to save things and hate losing things. When presented with the option of saving things, like money and lives, people avoid risks. When presented with a situation in which they might lose something, people are more willing to take risks. The interesting part is that the same situation can be presenting in terms of saving lives and losing lives. In terms of breast cancer, I suspect most of us think of screenings as saving lives. Delaying screenings seems risky. We don't want to risk those lives that could be saved with the extra screenings. That could be someone I know. I want the screening when her life could be saved. No risks desired when we are saving lives.

Our use of these and other reasoning heuristics is quick, easy, and often leads to decent decisions. With respect to breast cancer screenings, our heuristics conflict with the best evidence on when the tests can be most effectively applied. As a college professor who teaches statistics, I wish the Preventive Services Task Force the best of luck convincing people to overcome their reasoning biases and rely upon the statistical evidence. Unfortunately, the advice conflicts with our standard methods of making sense of the world.