Use of Factual Assumptions
In Hasan, as in many stroke cases, the evolution of the plaintiff’s symptoms over hours or days play a central role in the expert’s understanding of the nature of the stroke, the potential treatments available and the likelihood of success of a potential therapy. The facts required to accurately outline the evolution of symptoms may come from a number of sources including the medical records and imaging, but also from collateral sources such as the plaintiff themselves or friends or relatives who were with them when the stroke happened. Because an expert may not have access to all of this critical information through the records alone it may be beneficial to create a set of factual assumptions to assist them in forming their opinion. Because their opinion may rise and fall on that factual foundation, these assumptions must be created meticulously, and it is necessary to consider each fact and ensure that it can be proven at trial. In Hasan the court emphasized that “Where an expert mingles admissible and inadmissible evidence, the weight to be attributed to that opinion will be directly related to the amount and quality of admissible evidence on which the expert relies.“5 This was in play in Hasan as the court noted that the defence experts did not have a correct understanding of the progression of the plaintiff’s symptoms, which undermined their opinions both on the standard of care and on causation.6
The Expert’s Methodology
In weighing the expert opinions with respect to their review of the CT scans, the court considered the methodology employed by each expert to arrive at their conclusions.
Two of the plaintiff’s experts approached their review of the imaging “blindly” meaning they did not have preconceived theories about what might have occurred. Although the court wasn’t certain if the third plaintiff’s expert followed that same approach, the judge was impressed with that expert’s description of his process — he asked himself questions as he reviewed the imaging and matched up the imaging with the trajectory of the plaintiff’s symptoms.7
In contrast, one of the defence experts, the neurologist Dr. Silver, developed a theory about what might have happened based on particular features on imaging of December 8, then set about to prove his theory. As a result, he overlooked two other critical features on the imaging. The approach taken by the defence’s neuroradiologist, Dr. Krings, was also highlighted. Dr. Silver spoke with Dr. Krings and provided him with his theory of the case. The court did not suggest deliberate collusion, but was alive to the possibility of an unconscious or confirmation bias.8
The different methodology used by the experts for each side left the judge with greater confidence in the reliability of the plaintiff’s experts’ opinion. How you approach a potential expert at the beginning of your discussions with them has the potential to colour their approach to the case. As illustrated in the Hasan judgement, starting with a blank slate gives the expert the best chance of arriving at an opinion that will be viewed by the court as helpful and unbiased.