Misleading communication of riskBMJ 2010; 341 doi: https://doi.org/10.1136/bmj.c4830 (Published 12 October 2010) Cite this as: BMJ 2010;341:c4830
- Gerd Gigerenzer, director,
- Odette Wegwarth, research scientist,
- Markus Feufel, postdoctoral fellow
- 1Harding Center for Risk Literacy, Max Planck Institute for Human Development, Lentzeallee 94, 14195 Berlin, Germany
In 1996 a review of mammography screening reported in its abstract a 24% reduction of breast cancer mortality1; a review in 2002 claimed a 21% reduction.2 Accordingly, health pamphlets, websites, and invitations broadcast a 20% (or 25%) benefit.3 Did the public know that this impressive number corresponds to a reduction from about five to four in every 1000 women, that is, 0.1%? The answer is, no. In a representative quota sample in nine European countries, 92% of about 5000 women overestimated the benefit 10-fold, 100-fold, and more, or they did not know.4 For example, 27% of women in the United Kingdom believed that out of every 1000 women who were screened, 200 fewer would die of breast cancer. But it is not only patients who are misled. When asked what the “25% mortality reduction from breast cancer” means, 31% of 150 gynaecologists answered that for every 1000 women who were screened, 25 or 250 fewer would die⇓.3
In 1995, the UK Committee on Safety of Medicines issued a warning that third generation oral contraceptive pills increased the risk of potentially life …
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