Irren ist wahrscheinlich. Medizinische Experten und Laien bewerten Risiken oft falsch
Ulrich Hoffrage ()
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Ulrich Hoffrage: Sonderforschungsbereich 504, Postal: L 13, 15, D-68131 Mannheim
No 99-21, Sonderforschungsbereich 504 Publications from Sonderforschungsbereich 504, Universität Mannheim, Sonderforschungsbereich 504, University of Mannheim
Several studies have reported that physicians have great difficulties in estimating the positive predictive value of a diagnostic test, that is, the probability of a disease being present given a positive test. I argue that the problem lies not only in physiciansã lack of statistical training, but in the way numerical information is presented in such studies and in medical curricula. External representation is part¸ of the reasoning process. Specifically, when information is represented in natural frequencies, rather than in probabilities or percentages, diagnostic inferences improve¨without any instruction in statistics. In the study reported here, physicians with an average of 14 years professional experience profit from natural frequencies about as much as naive laypeople. When information was presented in terms of probabilities (the traditional way), the physicians correctly estimated the predictive value in only 10 of the cases. With natural frequencies, this percentage increased to 46. Representing information in natural frequencies is a quick, effective, and low-cost method of helping physicians, AIDS counselors, and other experts to communicate with clients about risks, and clients to better understand these risks.
Pages: 5 pages
Note: Financial Support from the Deutsche Forschungsgemeinschaft, SFB 504, at the University of Mannheim, is gratefully acknowledged.
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