Background: Patients and physicians often communicate using qualitative probability expressions that describe expected outcomes or risks of a medical intervention without knowing whether or not they share the same understanding.
Objective: The aim of the present study was to determine interpretations of qualitative probability expressions in clinical settings by Japanese patients and physicians as well as their assessments and preferences about physicians' use of such expressions.
Methods: One hundred and sixty-eight consecutive patients aged 16 years or older, who attended a university hospital during a 2-week period in 1999, and 156 physicians recruited through the Japanese General Medicine Research Network participated in this cross-sectional survey, using a self-administered questionnaire. Participants were asked to assign numerical interpretations as a percentage to 10 qualitative expressions of probability in two clinical situations related to prescribing a medicine for a cold and an anti-cancer drug. They were also asked which type of expression, qualitative or quantitative, they usually use when communicating probabilistic clinical information and which they prefer.
Results: The estimates of probability expressions showed wide variations, especially among patients. Patients tended to assign lower and higher values to highly positive and negative probability expressions, respectively, than physicians. Clinical context also influenced the estimation: both groups tended to assign higher estimates in the anti-cancer drug situation than in the cold treatment situation. Factor analysis revealed three psychologically meaningful factors in each situation. More patients than physicians (64.6% versus 50.3%) thought that physicians do not use numbers in routine practice. More than 20% of both patients and physicians considered that the actual use of qualitative terms by physicians is undesirable. Nevertheless, a sizable number of patients (41.4%) and physicians (15.2%) considered it preferable that physicians do not use numbers.
Conclusion: Since interpretation of qualitative expressions of probability in Japanese is subject to large interpersonal variability and differences between patients and physicians, as well as context dependence, the use of qualitative expressions alone might cause misunderstanding among the parties involved. However, the majority of patients prefer words to numbers at present. Therefore, physicians, at least in Japan, ought to provide patients with both numbers and words when critical decisions need to be communicated.