Diagnostic error is a common cause of medical malpractice action.  Hindsight is 20/20. 
 

With hindsight, the medical malpractice client and/or family will find it inconceivable that a competent clinician could have missed the diagnosis: after all, every textbook symptom and sign was present. 
 

Without hindsight, patients often present with an alphabet soup of complaints, anxieties, vulnerabilities, perceptions, interpretations - and the alert physician can see an alarmingly huge number of potential patterns that might be diagnoses. 

The diagnostic process, particularly in complex cases, is based on probablistic (Bayesian) reasoning.  That is to say, the clinician approaches diagnosis with a wealth of probability data - training and experience - that s/he progressively refines by history, clinical examination and investigations to develop the most likely diagnoses in this unique situation.  There is considerable uncertainty that is intrinsic to the process. 
 

Without hindsight bias, such probability can be a great deceiver.  During an influenza epidemic, the likelihood is very high that the next patient with headache, fever, and muscle aches will have influenza, and the probability is extremely low that s/he will have meningitis or bacterial endocarditis (when you hear hoof-beats, think horses not zebras.) 

If you need early diagnosis, a ‘flu’ epidemic - when the conscientious physician is trying to cope with a huge upsurge in demand for services and is focused on patient education - is not the best time to contract meningitis or develop bacterial endocarditis. 

Hindsight bias: people who know that an event has occurred overestimate their ability to previously predict that event.

The term hindsight bias was coined and formalised in 1975.  Historical events and psychotherapy case histories were the first material studied. 
 

Some research participants were, for instance, given information about the warring factions in the struggles between British soldiers and Gurka tribesmen, and were asked to attribute probabilities to various outcomes. 
 

Their responses were compared with those of other participants who were additionally given a supposed outcome.  Those who had been given hindsight overestimated their abilities to predict that outcome. 

In Medical Practice

Medical students, with continuous access to patients’ diagnoses, become overconfident in their own diagnostic ability and underestimate the difficulty in initially making those diagnoses. 

Clinico-Pathological Conferences are a powerful learning tool for medical undergraduates and postgraduates alike.  Each case is summarised from clinical presentation through detailed pathological diagnosis, including autopsy findings.  Participants are best served by being individually challenged to publicly weight the probable diagnoses before the definitive pathological results are disclosed. 

When providing second opinions, consulting physicians are overconfident in confirming diagnoses, and readily repeat the errors of their predecessors. 

In Medical Litigation

In the context of medical malpractice litigation, hindsight bias causes a medical expert’s mistaken belief: that, without hindsight, s/he would easily have been able to make a diagnosis. 

Mayo Clinic researchers studied a series of lung cancers that were diagnosed on chest radiographs. In 90% of cases, there were subtle abnormalities on earlier radiographs, that had originally been interpreted as normal. 

Thus the “community standard”, against which a malpractice defendant radiologist is judged, appears to be “missing” the early radiological signs of lung cancer. 

In a seminal US action [Gehlen v. Snohomish County Public Hospital. 98-2-01320-4 (Snohomish County, Wash. 2000)], both plaintiff and defence radiologist experts agreed that, having seen the later chest radiographs, they were able to pick out corresponding abnormalities on radiographs taken earlier in the illness and reported by the defendant as normal. 

However, the defence experts acknowledged that the changes were subtle and they would probably not have detected them without prior knowledge of the later radiographs. 

Having first been shown the obvious abnormalities on the later radiographs and then the subtle changes on the earlier films, the jury rejected the concept of hindsight bias and found for the plaintiff.  They apparently could not believe that a competent trained radiologist could not see without hindsight what was obvious to lay jurors who had the benefit of hindsight. 

Practical Implications

Colleagues of the defendant physician who has made an arguably negligent misdiagnosis may simply accept and perpetuate the diagnostic error. assuming perhaps  that the original diagnosis was reached by thorough and careful assessment.  The apparent endorsement by conscientious colleagues does not make the original error less negligent. 

When radiologists or anatomical pathologists are asked to comment on Standard of Care in misdiagnosis, they should be given no more - and no less - clinical information about the case than the defendant physician was given at the time.  In particular, they should be given no information about outcome.  Even so, the experts will inevitably be biased by the hindsight knowledge that diagnostic error has occurred. 

Ideally, any specialist providing medical malpractice expert opinion on clinical misdiagnosis should be given no more information than was available to the defendant physician at the time of the alleged negligence.  This does not represent current medicolegal practice. 

Medical malpractice jurors are instructed to consider only whether or not actions of the defendant physician fell below acceptable Standard of Care, and disregard whether damage ensued. 

In reality, determination of negligence is influenced by the hindsight that the patient sustained injury. The huge New York State study on prevalence of medical malpractice concluded that severity of injury, rather than evidence of substandard medical care, determined a finding of negligence. 

Hindsight bias is alive and well and living in our health-care system and courtrooms.  Just as claimants unconsciously revise their memories to favour Causation of symptoms following tortious injury, physicians unknowingly incorporate hindsight into their diagnostic and medicolegal judgments.