Simple tools for understanding risks: from innumeracy to insight

doi:10.1136/bmj.327.7417.741

BMJ 2003;327:741-744 (27 September), doi:10.1136/bmj.327.7417.741

Education and debate

Simple tools for understanding risks: from innumeracy to insight

Gerd Gigerenzer, director¹, Adrian Edwards, reader²

¹ Centre for Adaptive Behaviour and Cognition, Max Planck Institute for Human Development, Lentzeallee 94, 14195 Berlin, Germany, ² Primary Care Group, Swansea Clinical School, University of Wales Swansea, Swansea SA2 8PP

Correspondence to: G Gigerenzer gigerenzer@mpibberlin.mpg.de

Bad presentation of medical statistics such as the risks associatedwith a particular intervention can lead to patients making poordecisions on treatment. Particularly confusing are single eventprobabilities, conditional probabilities (such as sensitivityand specificity), and relative risks. How can doctors improvethe presentation of statistical information so that patientscan make well informed decisions?

The first 150 words of the full text of this article appear below.

The science fiction writer H G Wells predicted that in moderntechnological societies statistical thinking will one day beas necessary for efficient citizenship as the ability to readand write. How far have we got, a hundred or so years later?A glance at the literature shows a shocking lack of statisticalunderstanding of the outcomes of modern technologies, from standardscreening tests for HIV infection to DNA evidence. For instance,doctors with an average of 14 years of professional experiencewere asked to imagine using the Haemoccult test to screen forcolorectal cancer.^1
2 The prevalence of cancer was 0.3%, thesensitivity of the test was 50%, and the false positive ratewas 3%. The doctors were asked: what is the probability thatsomeone who tests positive actually has colorectal cancer? Thecorrect answer is about 5%. However, the doctors' answers rangedfrom 1% to 99%, with about half . . . [Full text of this article]

Single event probabilities

Conditional probabilities

Relative risks

The reference class

Framing

Manipulation

Conclusions

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