title: Natural Frequencies Do Not Foster Public Understanding of Medical Test Results.
abstract: Major organizations recommend presenting medical test results in terms of natural frequencies, rather than single-event probabilities. The evidence, however, is that natural frequency presentations benefit at most one-fifth of samples of health service users and patients. Only one study reported a substantial benefit of these presentations. Here, we replicate that study, testing online survey respondents. Study 1 attributed the previously reported benefit of natural frequencies to a scoring artifact. Study 2 showed that natural frequencies may elicit evaluations that conflict with the normatively correct one, potentially hindering informed decision making. Ironically, these evaluations occurred less often when respondents reasoned about single-event probabilities. These results suggest caution in promoting natural frequencies as the best way to communicate medical test data to health service users and patients.
authors.affiliation: Center for Experimental Research in Management and Economics, DCP, University IUAV of Venice, Venice, Italy (SP, VG)
authors.forename: Stefania
authors.initials: S
authors.lastname: Pighin
authors.affiliation: Laboratory of Cognitive Psychology, CNRS and Aix-Marseille University, Marseille, France (MG)
authors.forename: Michel
authors.initials: M
authors.lastname: Gonzalez
authors.affiliation: Department of Economics and Management, University of Trento, Trento, Italy (LS)
authors.forename: Lucia
authors.initials: L
authors.lastname: Savadori
authors.affiliation: Center for Experimental Research in Management and Economics, DCP, University IUAV of Venice, Venice, Italy (SP, VG)
authors.forename: Vittorio
authors.initials: V
authors.lastname: Girotto
mesh_terms: D000328:Adult; D000368:Aged; D003142:Communication; D003657:Decision Making; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010817:Physician-Patient Relations; D011336:Probability; D055815:Young Adult
keywords: diagnostic reasoning, numeracy; natural frequencies; single-event probability; test result understanding