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Cognitive biases


Influences on decision making

Influences on reasoning


Model of head with multiple words written on itCognitive bias is a way of thinking that influences reasoning and decision making, sometimes resulting in inaccurate judgments.

Cognitive biases (distortions of thinking) and affective biases (intrusion of the physician's feelings) may interfere significantly with reaching a correct diagnosis.

In recent years, many cognitive psychologists and physicians have studied diagnostic reasoning and decision making. [REF]
Lippincott, Williams, Wilkins, Cognitive and Affective Dispositions to Respond, Patient Safety in Emergency Medicine, 2009.

Sketch of head (side view) with gears insideWhat have they found?

  • Novices generally use a slower, analytical approach to reason out a diagnosis, often by gathering more information.

  • Experienced physicians often use an intuitive, pattern recognition approach — arriving rapidly and almost subconsciously at a best match for the patient's symptoms and signs, based on the physician's mental library of cases and syndromes.

    So when an experienced physician sees a skin rash, or a patient has a particular combination of symptoms and signs, or the physician recognizes a clinical syndrome or toxidrome, "pattern matching" is made to clinical templates previously established through the physician's experience.

    If no match occurs or the presentation is ambiguous, the physician may revert to analytical reasoning which requires a more deliberate, methodical approach.

  • While bias may affect all aspects of human reasoning, intuitive thinking is generally the most vulnerable.

    Many cognitive and affective biases are inter-related and more than one bias can affect the diagnosis of a patient. [REF]
    Scott, I., "Errors in clinical reasoning: causes and remedial strategies," BMJ, Vol. 339, p22-25.

  • Diagnosis by pattern recognition is quick, often very effective and usually correct, but is prone to interference by cognitive and affective biases that may occasionally mislead even the most experienced physicians.

  • Expert diagnosticians know when to revert from pattern recognition to analytical reasoning.

Irrespective of which method is used to arrive at a diagnosis, all diagnostic decisions are susceptible to cognitive biases. Many of these biases are inter-related: more than one bias can affect the diagnosis for an individual patient.