In the last blog post titled The causes and consequences of diagnostic failure, we reviewed the systemic and the no-fault causes of diagnostic failure. In this post we will explore the third class of diagnostic failure – that caused by cognitive factors. This group is important because of the frequency with which it contributes to diagnostic error. This is illustrated by a review of 100 cases of diagnostic failure carried out by Mark Graber and colleagues published in a paper titled Diagnostic error in internal medicine. In their analysis, they identified cognitive errors to be present in almost 75% of cases of diagnostic failure.

Pat  Croskerry broadly classified cognitive diagnostic errors into two in the book Advances in Patient Safety: From Research to Implementation (Volume 2: Concepts and Methodology). The first class consists of errors of ignorance in which the mistakes arise from the doctor’s poorly calibrated knowledge or skills, and the second group is made up of errors of implementation where the fault can be traced to the doctor’s impaired physical or mental state.

Errors of ignorance have a diverse list of causes, and many of these are discussed by Arthur Elstein and Alan Schwarz in their paper titled Clinical problem solving and diagnostic decision making: selective review of the cognitive literature. They specifically highlighted the following:

• • Faulty knowledge
  • Inadequate knowledge
  • Misperception or misreading of the data
  • Misinterpretation of the data
  • Misjudging the salience of findings
  • Failure to generate the correct hypotheses
  • Failure to consider reasonable alternative diagnoses
  • Premature closure of the diagnosis

Errors of ignorance may also be classified by the different stages of the diagnostic process which they compromise. Two papers which have explored this in detail are Missed and delayed diagnoses in the ambulatory setting: a study of closed malpractice claims by Tejal Gandhi and colleagues, and Diagnostic error in medicine: analysis of 583 physician-reported errors by Gordon Schiff and colleagues. The errors of ignorance both papers highlighted were:

• • Failure to take adequate history
  • Failure to perform an adequate physical examination
  • Failure to order an appropriate diagnostic test
  • Failure to correctly interpret diagnostic tests
  • Failure to arrange appropriate follow-up
  • Failure to order, report, or follow-up test results
  • Delays in referral or consultation

• • Fatigue
  • Stress
  • Sleep deprivation
  • Poor motivation
  • Ill health
  • Marital conflict
  • Family loss
  • Circadian dys-synchronicity – the effect of winter months or shift work
  • Countertransference – the effect of the patient’s mood 

Croskerry also explored other biological factors beyond mood which impair the decision-making process. Amongst these are:

• • The doctor’s biases regarding gender and race
  • The doctor’s personal preferences towards the anticipated goodness of the diagnostic outcome -what the doctor hopes will happen
  • The doctor’s preference towards the anticipated failure of the outcome – what the doctor fears might happen

The other factors which Corskerry discussed are those which operate to impair the decision-making of teams, and these included:

• • Interpersonal conflict
  • Low morale
  • Group think
  • Normalisation of deviance – ‘the accumulated tolerance of unsafe conditions that develops over time and ultimately compromises patient safety‘.

In the next blog post, we will take a step further into the biological drivers of diagnostic failure and look at the diagnostic perils of overconfidence.