Natural-frequency approach may be superior for training people to interpret health tests, judge courtroom evidence and more

WASHINGTON Does a positive mammogram mean a woman has breast cancer? Does a positive HIV test mean someone is infected with the virus? As ordinary people confront the laws of probability, the odds of misinterpretation and false alarms rise. Two German psychologists have found a better way to teach basic statistical concepts, based on the way people naturally weigh the odds. This approach can help patients, and the doctors who advise them, more accurately assess the meaning of test results.

Peter Sedlmeier, Ph.D., of the Chemnitz University of Technology and Gerd Gigerenzer, Ph.D., of the Max Planck Institute for Human Development in Berlin, tested their approach using computer-based tutorials that cover basic binary statistical literacy (the outcome is either this or that), that took students up to two hours to complete. The psychologists findings appear in the September issue of the Journal of Experimental Psychology: General, published by the American Psychological Association (APA).

In their article, Sedlmeier and Gigerenzer contrast two approaches to statistical training. Percentage-based rules would state, for example (using hypothetical numbers), If a woman undergoing mammography has breast cancer, the probability that she will test positive is 80%. Natural-frequency rules would state, using the same example, Eight of every 10 women with breast cancer who undergo mammography will test positive. Whereas Percentages view probabilities in light of a fixed number, 100, natural frequencies dont share a common norm.

Still, the authors predicted that the latter approach would be easier for people to learn because it taps a natural ability to count the observable, without having to use symbolic abstraction. Previous research has shown that people calculate the odds of any given event more e
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16-Sep-2001