Applied Evidence

Cognitive bias: Its influence on clinical diagnosis

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In a busy practice, it’s helpful to be aware of specific psychological tendencies that influence diagnostic reasoning and can lead to error.


› Acquire a basic understanding of key cognitive biases to better appreciate how they could interfere with your diagnostic reasoning. C

› Consider using a differential diagnosis generator as a safeguard if you suspect an increased risk of diagnostic error in a particular patient. C

Strength of recommendation (SOR)

A Good-quality patient-oriented evidence
B Inconsistent or limited-quality patient-oriented evidence
C Consensus, usual practice, opinion, disease-oriented evidence, case series



CASEA patient with a history of drug-seeking behavior asks to be seen by you for lower back pain. Your impression upon entering the examination room is that the patient appears to be in minimal pain. A review of the patient’s chart leads you to suspect that the patient’s past behavior pattern is the reason for the visit. You find yourself downplaying his reports of weight loss, changed bowel habits, and lower extremity weakness—despite the fact that these complaints might have led you to consider more concerning causes of back pain in a different patient.

This situation is not uncommon. At one time or another, it’s likely that we have all placed an undue emphasis on a patient’s social background to reinforce a pre-existing opinion of the likely diagnosis. Doing so is an example of both anchoring and confirmation biases—just 2 of the many biases known to influence critical thinking in clinical practice (and which we’ll describe in a bit).

Reconsidering the diagnostic process. Previous attempts to address the issue of incorrect diagnosis and medical error have focused on systems-based approaches such as adopting electronic medical records to avert prescribing errors or eliminating confusing abbreviations in documentation.1 However, greater attention is being given to understanding the cognitive processes of medical providers, acknowledging that many diagnostic errors result from faulty reasoning rather than a lack of knowledge.1

Graber et al reviewed 100 errors involving internists and found that 46% of the errors resulted from a combination of systems-based and cognitive reasoning factors.2 More surprisingly, 28% of errors were attributable to reasoning failures alone.2 Singh et al showed that in one primary care network, most errors occurred during the patient-doctor encounter, with 56% involving errors in history taking and 47% involving oversights in the physical examination.3 Furthermore, most of the errors occurred in the context of common conditions such as pneumonia and congestive heart failure—rather than esoteric diseases—implying that the failures were due to errors in the diagnostic process rather than from a lack of knowledge.3

An understanding of the diagnostic process and the etiology of diagnostic error is of utmost importance in primary care. Family physicians who, on a daily basis, see a high volume of patients with predominantly low-acuity conditions, must be vigilant for the rare life-threatening condition that may mimic a more benign disease. It is in this setting that cognitive errors may abound, leading to both patient harm and emotional stress in physicians.3

This article reviews the current understanding of the cognitive pathways involved in diagnostic decision making, explains the factors that contribute to diagnostic errors, and summarizes the current research aimed at preventing these errors.

Continue to: The diagnostic process, as currently understood


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