USING NATURAL FREQUENCIES TO IMPROVE DIAGNOSTIC INFERENCES

Purpose. To test whether physicians' diagnostic inferences can be impr oved by communicating information using natural frequencies instead of probabilities. Whereas probabilities and relative frequencies are nor malized with respect to disease base rates, natural frequencies are no t normalized. Method. The authors asked 48 physicians in Munich and Du sseldorf to determine the positive predictive values (PPVs) of four di agnostic tests. Information presented in the four problems appeared ei ther as probabilities (the traditional way) or as natural frequencies. Results. When the information was presented as probabilities, the phy sicians correctly estimated the PPVs in only 10% of cases. When the sa me information was presented as natural frequencies, that percentage i ncreased to 46%. Conclusion. Representing information in natural frequ encies is a fast and effective way of facilitating diagnostic insight, which in rum helps physicians to better communicate risks to patients , and patients to better understand these risks.