Dan Goldstein at Decision Science News has just highlighted some interesting stuff from Gerd Gigerenzer in relation to the perceived value of cancer screening. Gigerenzer recently authored Gut Feelings: The Intelligence of the Unconscious, which I reviewed here. Gigerenzer demonstrates the problem of false positives, the fear it can induce in the unlucky patient, and also the concept of “relative risk reduction”. Clinicians themselves get these values wrong (by a factor of 10 in the case of mammogram false positives), and can convey the wrong message to patients.

Meanwhile, in representing the value of screening, breast cancer screening is said to reduce the risk of dying by 25 per cent. And yet the difference is actually 3 out of 1000 screened women will die, compared with 4 out of 1000 unscreened patients — an absolute reduction of 0.1 per cent, but a relative reduction of 25 per cent. Interestingly, some risk of contracting cancer from mammography is introduced.

Gigerenzer shows that a more psychologically-informed approach can lead to better decision-making and communication.

Cancer information brochures, for example, provide a great challenge. Most brochures in the United States and in Europe do not present medical research candidly. For instance, benefits are often presented as relative risk reductions, as they are bigger figures, whereas potential harms, if mentioned at all, are reported in less impressive absolute risks, such as that one out of 1,000 women will contract mammogram-induced breast cancer. A few health organizations have responded to our work and reworded their publications accordingly, whereas representatives of others have openly told me that their primary goal is to foster compliance, not comprehension.

Journalists, who frequently don’t sufficiently scrutinize different statistical measurements when offered them, should take note of how easily they can be misled by government in this domain:-

Strong resistance to transparency also comes from governments. In response to my book Calculated Risks (2002), Karl Lauterbach, then an advisor to the German Minister of Health and now a member of the German parliament, publicly defended the ministry’s use of relative risks. He stated that the ministry’s responsibility is to inform the general public, not individual women, and that only doctors should inform patients in terms of absolute risks. If this distinction seems as arbitrary to you as it is to me, it might help to know that, with the help of the 25 percent (and even a 35 percent) figure, the German parliament was persuaded to pass a law ensuring women aged 50-69 free access to mammography screening. Yet conflicts of interest are not limited to Germany alone. A few years ago, I presented the program of transparent risk communication to the National Cancer Institute in Bethesda, MD. Two officials took me aside afterwards and lauded the program for its potential to make healthcare more rational. I asked if they intended to implement it. Their answer was “no.” And why not? As they explained, transparency in this form was bad news for the government — a benefit of only 0.1 percent instead of 25 percent would make poor headlines for the upcoming election! In addition, their board was staffed by the presidential administration, for whom transparency in health care was not (and is not) a priority.”

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