title: The biasing effect of clinical history on physical examination diagnostic accuracy.
abstract: BACKGROUND
  Literature on diagnostic test interpretation has shown that access to clinical history can both enhance diagnostic accuracy and increase diagnostic error. Knowledge of clinical history has also been shown to enhance the more complex cognitive task of physical examination diagnosis, possibly by enabling early hypothesis generation. However, it is unclear whether clinicians adhere to these early hypotheses in the face of unexpected physical findings, thus resulting in diagnostic error.
  
  
  METHODS
  A sample of 180 internal medicine residents received a short clinical history and conducted a cardiac physical examination on a high-fidelity simulator. Resident Doctors (Residents) were randomised to three groups based on the physical findings in the simulator. The concordant group received physical examination findings consistent with the diagnosis that was most probable based on the clinical history. Discordant groups received findings associated with plausible alternative diagnoses which either lacked expected findings (indistinct discordant) or contained unexpected findings (distinct discordant). Physical examination diagnostic accuracy and physical examination findings were analysed.
  
  
  RESULTS
  Physical examination diagnostic accuracy varied significantly among groups (75 ± 44%, 2 ± 13% and 31 ± 47% in the concordant, indistinct discordant and distinct discordant groups, respectively (F(2,177)  = 53, p < 0.0001). Of the 115 Residents who were diagnostically unsuccessful, 33% adhered to their original incorrect hypotheses. Residents verbalised an average of 12 findings (interquartile range: 10-14); 58 ± 17% were correct and the percentage of correct findings was similar in all three groups (p = 0.44).
  
  
  CONCLUSIONS
  Residents showed substantially decreased diagnostic accuracy when faced with discordant physical findings. The majority of trainees given discordant physical findings rejected their initial hypotheses, but were still diagnostically unsuccessful. These results suggest that overcoming the bias induced by a misleading clinical history may involve two independent steps: rejection of the incorrect initial hypothesis, and selection of the correct diagnosis. Educational strategies focused solely on prompting clinicians to re-examine their hypotheses may be insufficient to reduce diagnostic error.
authors.affiliation: Division of Cardiology, Department of Medicine, Faculty of Medicine, University of Toronto, Ontario, Canada. mattsibbald@gmail.com
authors.forename: Matthew
authors.initials: M
authors.lastname: Sibbald
authors.forename: Rodrigo B
authors.initials: RB
authors.lastname: Cavalcanti
mesh_terms: D000704:Analysis of Variance; D002983:Clinical Competence / Q000592:standards*; D003937:Diagnosis, Differential; D003951:Diagnostic Errors / Q000517:prevention & control*; D004503:Education, Medical, Graduate / Q000379:methods* / Q000592:standards; D006801:Humans; D008487:Medical History Taking / Q000379:methods / Q000592:standards*; D010808:Physical Examination / Q000592:standards*; D011897:Random Allocation; D013663:Teaching / Q000379:methods