gerd_gigerenzer's picture
Psychologist; Director, Harding Center for Risk Literacy, Max Planck Institute for Human Development; Author, How to Stay Smart in a Smart World
The Advent of Health Literacy

In a 2007 radio advertisement, former NYC mayor Rudy Giuliani said, "I had prostate cancer, five, six years ago. My chances of surviving prostate cancer — and thank God I was cured of it — in the United States: 82 percent. My chances of surviving prostate cancer in England: only 44 percent under socialized medicine." Giuliani was lucky to be living in New York, and not in York — true?

In World Brain (1938), H. G. Wells predicted that for an educated citizenship in a modern democracy, statistical thinking would be as indispensable as reading and writing. At the beginning of the 21st century, we have succeeded in teaching millions how to read and write, but many of us still don't know how to reason statistically — how to understand risks and uncertainties in our technological world.

Giuliani is a case in point. One basic concept that everyone should understand is the 5-year survival rate. Giuliani used survival rates from the year 2000, where 49 Britons per 100,000 were diagnosed of prostate cancer, of which 28 died within 5 years — about 44 percent. Is it true that his chances of surviving cancer are about twice as high in what Giuliani believes is the best health care system in the world? Not at all. Survival rates are not the same as mortality rates. The U.S. has in fact about the same prostate cancer mortality rate as the U.K. But far more Americans participate in PSA screening (although its effect on mortality reduction has not been proven). As a consequence, more Americans are diagnosed of prostate cancer, which skyrockets the 5-year survival rate to more than 80%, although no life is saved. Screening detects many "silent" prostate cancers that the patient would have never noticed during his lifetime. Americans live longer with the diagnosis, but they do not live longer. Yet many Americans end up incontinent or impotent for the rest of their lives, due to unnecessary aggressive surgery or radiation therapy, believing that their life has been saved.

Giuliani is not an exception to the prevailing confusion about how to evaluate health statistics. For instance, my research shows that 80% to 90% of German physicians do not understand what a positive screening test means — such as PSA, HIV, or mammography — and most do not know how to explain the patient the potential benefits and harms. Patients however falsely assume that their doctors know and understand the relevant medical research. In most medical schools, education in understanding health statistics is currently lacking or ineffective.

The bare fact of statistical illiteracy among physicians, patients, and politicians is still not well known, much less addressed, made me pessimistic about the chances of any improvement. Statistical illiteracy in health matters turns the ideals of informed consent and shared decision-making into science fiction. Yet I have begun to change my mind. Here are a few reasons why I'm more optimistic.

Consider the concept of relative risks. You may have heard that mammography screening reduces breast cancer mortality by 25%! Impressive, isn't it? Many believe that if 100 women participate, the life of 25 will be saved. But don't be taken in again. The number is based on studies that showed that out of every 1,000 women who do not participate in mammography screening, 4 will die of breast cancer within about 10 years, whereas among those who participate in screening this number decreases to 3. This difference can be expressed as anabsolute risk, that is, one out of every 1,000 women dies less of breast cancer, which is a clear and transparent.  But it also can be phrased in terms of a relative risk: a 25% benefit. I have asked hundreds of gynecologists to explain what this benefit figure means. The good news is that two-thirds understood that 25% means 1 in 1,000. Yet one third overestimated the benefits by one or more orders of magnitudes. Thus, better training in medical school is still wanted.

What makes me optimistic is the reaction of some 1,000 gynecologists I have trained in understanding risks and uncertainties as part of their continuing education. First, learning how to communicate risks was a top topic on their wish list. Second, despite the fact that most had little statistical training, they learned quickly. Consider the situation of a woman who tests positive in a screening mammogram, and asks her doctor whether she has cancer for certain, or what her chances are.  She has a right to get the best answer from medical science: Out of ten women who test positive, only one has breast cancer, the other nine cases are false alarms. Most women are never informed about this relevant fact, and react with panic and fear. Mammography is not a very reliable test. Before the training, the majority of gynecologists mistakenly believed that about 9 out of 10 women who test positive have cancer, as opposed to only one! After the training, however, almost all physicians understood how to read this kind of health statistics. That's real progress, and I didn't expect so much, so soon.

What makes me less optimistic is resistance to transparency in health from government institutions. A few years ago, I presented the program of transparent risk communication to the National Cancer Institute in Bethesda. Two officials took me aside afterwards and lauded the program for its potential to make health care more rational. I asked if they intended to implement it. Their answer was no. Why not? As they explained, transparency in this form was bad news for the government — a benefit of only 0.1% instead of 25% would make poor headlines for the upcoming election! In addition, their board was appointed by the presidential administration, for which transparency in health care is not a priority.

Win some, lose some. But I think the tide is turning. Statistics may still be woefully absent from most school curricula, including medical schools. That could soon change in the realm of health, however, if physicians and patients make common cause, eventually forcing politicians to do their homework.