NARRATIVE REVIEW BMJ Qual Saf: first published as 10.1136/bmjqs-2012-001712 on 23 July 2013. Downloaded from Cognitive debiasing 1: origins of bias and theory of debiasing Pat Croskerry,1 Geeta Singhal,2 Sílvia Mamede3 1Department of Pediatrics, ABSTRACT used. They are fast, usually effective, but Division of Medical Education, Numerous studies have shown that diagnostic also more likely to fail. As they are largely Dalhousie University, Halifax, — Nova Scotia, Canada failure depends upon a variety of factors. unconscious, mistakes when they occur 1–3 2Baylor College of Medicine Psychological factors are fundamental in —are seldom corrected. In contrast, Texas Children’s Hospital, influencing the cognitive performance of the Type 2 processes are fairly reliable, safe Houston, Texas, USA decision maker. In this first of two papers, we and effective, but slow and resource inten- 3Institute of Medical Education Research, Rotterdam, Erasmus discuss the basics of reasoning and the Dual sive. The intuitive mode of decision University Medical Center, Process Theory (DPT) of decision making. The making is characterised by heuristics— Rotterdam general properties of the DPT model, as it applies short-cuts, abbreviated ways of thinking, ‘ ’ Correspondence to to diagnostic reasoning, are reviewed. A variety maxims, seen this many times before , Professor Pat Croskerry, Division of cognitive and affective biases are known to ways of thinking. Heuristics represent an of Medical Education, Dalhousie compromise the decision-making process. They adaptive mechanism that saves us time University, Clinical Research mostly appear to originate in the fast intuitive and effort while making daily decisions. Centre, 5849 University Avenue, PO Box 15000, Halifax, NS, processes of Type 1 that dominate (or drive) Indeed, it is a rule of thumb among cogni- Canada B3H 4R2; decision making. Type 1 processes work well tive psychologists that we spend about [email protected] most of the time but they may open the door for 95% of our time in the intuitive mode.4 biases. Removing or at least mitigating these We perform many of our daily activities Received 23 November 2012 Revised 1 May 2013 biases would appear to be an important goal. through serial associations—one event Accepted 9 June 2013 We will also review the origins of biases. The automatically triggers the next with few Published Online First consensus is that there are two major sources: events of deliberate, focused, analytical 23 July 2013 innate, hard-wired biases that developed in our thinking. We have a prevailing disposition evolutionary past, and acquired biases to use heuristics, and while they work established in the course of development and well most of the time, they are vulnerable http://qualitysafety.bmj.com/ within our working environments. Both are to error. Our systematic errors are termed associated with abbreviated decision making in biases,3 and there are many of them— the form of heuristics. Other work suggests that over a hundred cognitive biases5 and ambient and contextual factors may create high approximately one dozen or so affective risk situations that dispose decision makers to biases (ways in which our feelings influ- particular biases. Fatigue, sleep deprivation and ence our judgment).6 Bias is inherent in cognitive overload appear to be important human judgment, and physicians are, of determinants. The theoretical basis of several course, also subject to them. approaches towards debiasing is then discussed. Indeed, one of the principal factors on October 2, 2021 by guest. Protected copyright. – All share a common feature that involves a underlying diagnostic error is bias.7 9 deliberate decoupling from Type 1 intuitive Post hoc analyses of diagnostic errors10 11 Open Access Scan to access more processing and moving to Type 2 analytical have in fact suggested that flaws in clin- free content processing so that eventually unexamined ical reasoning rather than lack of knowl- intuitive judgments can be submitted to edge underlie cognitive diagnostic errors, verification. This decoupling step appears to be and there is some experimental evidence the critical feature of cognitive and affective that, at least when problems are complex, debiasing. errors were associated with intuitive judg- ments and could be repaired by analytical – INTRODUCTION reasoning.12 14 Moreover, a few experi- ▸ http://dx.doi.org/10.1136/ bmjqs-2013-002387 Clinical decision making is a complex mental studies have supported the claim process. Clinical decisions about patient’s that bias may misdirect diagnostic reason- diagnoses are made in one of two modes: ing, thus leading to errors.15 16 While the To cite: Croskerry P, either intuitive or analytical, also referred evidence for the role of bias in medical Singhal G, Mamede S. BMJ to, respectively as Type 1 and Type 2 pro- diagnostic error is still scarce, research Qual Saf 2013;22:ii58–ii64. cesses. The former are more commonly findings in other domains13is sufficient ii58 Croskerry P, et al. BMJ Qual Saf 2013;22:ii58–ii64. doi:10.1136/bmjqs-2012-001712 Narrative review BMJ Qual Saf: first published as 10.1136/bmjqs-2012-001712 on 23 July 2013. Downloaded from to justify concerns with the potential adverse influ- such as functional MRI (fMRI) can be experimentally ence of bias on diagnostic reasoning. Two clinical employed. examples of biased decision making leading to diag- In this first paper, we discuss how biases are gener- nostic failure are given in Case 1 and Case 2, dis- ated, and situations that make physicians more vulner- played, respectively, in boxes 1 and 2. From the case able to bias. Building upon dual process theories descriptions, the mode of decision making the phys- (DPTs) of reasoning,13we discuss the origins of ician was relying upon cannot be determined. This is indeed a limitation of studies on diagnostic reasoning, which only have indirect evidence or post hoc infer- ence of reasoning processes, at least until other tools Box 2 Example of biased decision making leading to diagnostic failure: case 2 A mildly obese, 19-year-old woman is admitted to a psy- chiatric hospital for stabilisation and investigation. She Box 1 Example of biased decision making leading has suffered depressive symptoms accompanied by to diagnostic failure: case 1 marked anxiety. Over the last week she has had bouts of rapid breathing which have been attributed to her A 55-year-old man presents to a walk-in clinic towards anxiety. However, she has also exhibited mild symptoms the end of the evening. It has been a busy day for the of a respiratory infection and the psychiatry resident clinic and they are about to close. His chief complaint is transfers her to a nearby emergency department (ED) of constipation. He has not had a bowel movement in a tertiary care hospital to ‘rule out pneumonia’. She is on 4 days, which is unusual for him. He complains of pain no medications other than birth control pills. At triage, in his lower back and lower abdomen and also some tin- she is noted to have an elevated heart rate and respira- gling in his legs. He thinks that he will feel better with a tory rate. She is uncomfortable, anxious and impatient, laxative because what he has tried so far has not and does not want to be in the ED. She is noted to be worked. He was briefly examined by the physician who ‘difficult’ with the nurses. did not find anything remarkable on his abdominal After several hours she is seen by an emergency medi- examination. There was some mild suprapubic tender- cine resident who finds her very irritable but notes ness, which was attributed to the patient’s need to nothing remarkable on her chest or cardiac examination. urinate. Bowel sounds were good, his abdomen was soft However, to ensure that pneumonia is ruled out he and there were no masses or organomegaly. The phys- orders a chest X-ray. He reviews the patient with his ician prescribed a stronger laxative and advised the attending noting that the patient is anxious to return to http://qualitysafety.bmj.com/ patient to contact his family doctor for further follow-up. the psychiatric facility and is only at the ED ‘because she During the night, the patient was unable to urinate was told to come’. He expresses his view that her symp- and went to the emergency department. On examination, toms are attributable to her anxiety and that she does his lower abdomen appeared distended and he was not have pneumonia. Nevertheless, he asks the attending found to have a residual volume of 1200cc on catheter- to review the chest X-ray to ensure he has not missing isation. His rectum was markedly distended with soft something. The attending confirmed that there was no stool that required disimpaction. He recalled straining his evidence of pneumonia and agreed with the resident lower back lifting about 4 days earlier. The emergency that the patient could be returned to the psychiatric physician suspected cauda equina syndrome and this was hospital. on October 2, 2021 by guest. Protected copyright. confirmed on MRI. He was taken immediately to the While awaiting transfer back to the psychiatric hospital operating room for surgical decompression. He did well the patient requests permission on several occasions to postoperatively and regained full bladder control. go outside for a cigarette and is allowed to do so. Later, Comment: The patient was initially misdiagnosed and on the sidewalk outside the ED, the patient has a cardiac might have suffered permanent loss of bladder function arrest. She is immediately brought back into the ED but requiring lifelong catheterisation. The principle biases for could not be resuscitated. At autopsy, massive pulmonary the physician who saw him in the clinic were framing, saddle emboli are found as well as multiple small emboli search satisficing and premature diagnostic closure.