Background: A substantial proportion of diagnostic errors in medicine can be attributed to faults in physician’s cognitive processes. Research on medical expertise suggests that physician’s reasoning may be susceptible to bias, such as confirmation bias (i.e., the tendency to seek information to support rather than refute a hypothesis). The present study attempts to explore confirmatory tendencies in medical diagnosis. It is hypothesized that physicians tend to focus on and therefore report more clinical features that support a diagnosis that has been suggested to them, while ignoring features that speak against the suggested diagnosis.
Methods: Thirty-eight internal medicine residents accepted or rejected suggested diagnoses on 4 written randomly presented clinical cases. Two of those suggested diagnoses, which were also randomized among the cases, were correct and 2 were incorrect for each participant. After evaluating each suggestion, participants reported the features they would mention to a supervisor while discussing the patient. It was hypothesized that the reported features would be corroborative of the suggested diagnoses.
Results: Participants had more trouble rejecting incorrect suggestions (correct evaluation score on cases with incorrect suggestions: M = .63, SD = .59) than accepting correct suggestions (M = 1.13, SD = .70), t(37) = 2.84, p < .05, d = .77. Irrespective of the correctness of the suggested diagnosis, a significantly higher percentage of features supporting the suggested diagnoses (M = 39.05, SD = 12.70) was reported than features supportive of the alternative diagnosis (M = 25.25, SD = 13.33), t(37) = 4.40, p < .05, d = 1.06. This reporting was irrespective of the participants’ diagnostic decisions. Furthermore, when incorrect suggestions were accepted, more features supportive of these suggestions were reported than when they were rejected, t(49) = 1.88, p < .05, d = .53, which may indicate a confirmation bias.
Conclusion: These findings demonstrate that the tendency to confirm suggested diagnoses is mediated by a focus on features that support these suggestions. This tendency may lead to diagnostic errors when the suggestion is incorrect.