Natural Frequencies Do Not Foster Public Understanding of Medical Test Results

Med Decis Making. 2016 Aug;36(6):686-91. doi: 10.1177/0272989X16640785. Epub 2016 Mar 31.


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.

Keywords: diagnostic reasoning, numeracy; natural frequencies; single-event probability; test result understanding.

MeSH terms

  • Adult
  • Aged
  • Communication*
  • Decision Making
  • Female
  • Humans
  • Male
  • Middle Aged
  • Physician-Patient Relations*
  • Probability
  • Young Adult