Article Text

Immunising’ physicians against availability bias in diagnostic reasoning: a randomised controlled experiment
  1. Sílvia Mamede1,2,
  2. Marco Antonio de Carvalho-Filho3,4,
  3. Rosa Malena Delbone de Faria5,6,
  4. Daniel Franci3,
  5. Maria do Patrocinio Tenorio Nunes7,
  6. Ligia Maria Cayres Ribeiro8,
  7. Julia Biegelmeyer7,
  8. Laura Zwaan1,
  9. Henk G Schmidt1,2
  1. 1 Institute of Medical Education Research Rotterdam, Erasmus MC, Rotterdam, Zuid-Holland, The Netherlands
  2. 2 Psychology, Education and Child Studies, Erasmus University Rotterdam, Rotterdam, Zuid-Holland, The Netherlands
  3. 3 Internal Medicine, State University of Campinas, Campinas, Brazil
  4. 4 Center for Education Development and Research in the Health Professions, University of Groningen, Groningen, The Netherlands
  5. 5 Propeudeutics, Federal University of Minas Gerais, Belo Horizonte, Brazil
  6. 6 Education and Research Center, Santa Casa BH, Belo Horizonte, Minas Gerais, Brazil
  7. 7 Internal Medicine, Universidade de São Paulo, Sao Paulo, Brazil
  8. 8 Department of Medical Education Development, UNIFENAS Medical School, Belo Horizonte, Brazil
  1. Correspondence to Dr Sílvia Mamede, Institute of Medical Education Research Rotterdam, Erasmus MC, Rotterdam 3015CN, The Netherlands; s.mamede{at}


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.

  • cognitive biases
  • diagnostic errors
  • medical education
  • patient safety

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  • Contributors All authors had full access to all the study data and take responsibility for the integrity of the data and the accuracy of the data analysis. Study conception and design: SM, LZ, HGS. Development of study materials: SM, MACF, DF, MPTN, JB. Acquisition of data: SM, MACF, RMDF, DF, MPTN, LMCR, JB. Analysis or interpretation of data: All authors. Drafting of the manuscript: SM, HGS. Critical revision of the manuscript for important intellectual content: All authors. Statistical analysis: SM, HGS. Administrative, technical or material support: SM, MACF, RMDF, DF, MPTN, LMCR, JB. Supervision: SM, HGS.

  • Funding The universities and teaching hospitals involved in the study provided materials and facilities for the data collection.

  • Disclaimer The funding institutions had no role in the design and conduct of the study; collection, analysis and interpretation of data; preparation, review or approval of the manuscript; and decision to submit the manuscript for publication.

  • Competing interests None declared.

  • Patient consent for publication Not required.

  • Ethics approval The study was approved by the University of São Paulo Institutional Review Board and registered on the National Research Ethics platform (#68745917.1.1001.0068) as a multicentre study.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data availability statement Data are available upon reasonable request. Data availability is subject to the requirements of the existing policies for data management adopted by the institutions involved in the study.

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