Abstract
BACKGROUND: Diagnostic errors have often been attributed to biases in physicians' reasoning. Interventions to 'immunise' physicians against bias have focused on improving reasoning processes and have largely failed. OBJECTIVE: To investigate the effect of increasing physicians' relevant knowledge on their susceptibility to availability bias. DESIGN, SETTINGS AND PARTICIPANTS: Three-phase multicentre randomised experiment with second-year internal medicine residents from eight teaching hospitals in Brazil. INTERVENTIONS: Immunisation: Physicians diagnosed one of two sets of vignettes (either diseases associated with chronic diarrhoea or with jaundice) and compared/contrasted alternative diagnoses with feedback. Biasing phase (1 week later): Physicians were biased towards either inflammatory bowel disease or viral hepatitis. Diagnostic performance test: All physicians diagnosed three vignettes resembling inflammatory bowel disease, three resembling hepatitis (however, all with different diagnoses). Physicians who increased their knowledge of either chronic diarrhoea or jaundice 1 week earlier were expected to resist the bias attempt. MAIN OUTCOME MEASUREMENTS: Diagnostic accuracy, measured by test score (range 0-1), computed for subjected-to-bias and not-subjected-to-bias vignettes diagnosed by immunised and not-immunised physicians. RESULTS: Ninety-one residents participated in the experiment. Diagnostic accuracy differed on subjected-to-bias vignettes, with immunised physicians performing better than non-immunised physicians (0.40 vs 0.24; difference in accuracy 0.16 (95% CI 0.05 to 0.27); p=0.004), but not on not-subjected-to-bias vignettes (0.36 vs 0.41; difference -0.05 (95% CI -0.17 to 0.08); p=0.45). Bias only hampered non-immunised physicians, who performed worse on subjected-to-bias than not-subjected-to-bias vignettes (difference -0.17 (95% CI -0.28 to -0.05); p=0.005); immunised physicians' accuracy did not differ (p=0.56). CONCLUSIONS: An intervention directed at increasing knowledge of clinical findings that discriminate between similar-looking diseases decreased physicians' susceptibility to availability bias, reducing diagnostic errors, in a simulated setting. Future research needs to examine the degree to which the intervention benefits other disease clusters and performance in clinical practice. TRIAL REGISTRATION NUMBER: 68745917.1.1001.0068.