Expert Evidence: What is it, and why does it matter?

Expert evidence is often used in many areas of the law. It is particularly important in medical malpractice cases. Expert evidence is described in the case law as opinion evidence on a technical, scientific, or specialized subject or matter. The purpose of this evidence is to assist either the judge or jury in a subject matter outside the scope of understanding of the general population.

Generally, opinion evidence (when someone offers their opinion on the issue in court) is not permitted in a court of law. Since expert evidence is in-fact opinion evidence, there are four requirements which it must meet in order to be admissible: the expert evidence must be relevant to the case and the issue before the court, the evidence must be necessary to assist the judge or jury in understanding the matter and drawing the correct inference, the evidence must not be barred from admission by the application of other rules of evidence, and the evidence must be given by a qualified expert. For an expert to be qualified, they must be impartial, unbiased, and independent, in addition to having the requisite skill, knowledge, and experience to give evidence on the relevant subject matter.

Why is expert evidence important in medical malpractice cases? To be successful in a case involving medical malpractice, the plaintiff (the injured party/patient), must prove that the Defendant (health care professional), breached the standard of care, causing their injury to occur. That is, the Plaintiff must prove that the health care professional acted in a manner which was not reasonable in the circumstances. They then must prove that it was because of the Defendant’s unreasonable actions (or inactions) that the Plaintiff suffered their injuries.

Medical malpractice cases often involve very complex medical issues. Since the general public does not have the medical knowledge needed to know what actions a health care professional should take in certain situations, we rely on expert evidence to inform the judge or jury of this. The expert will assist the judge or jury in determining what was the appropriate standard of care – what would the reasonable health care professional have done in these circumstances. They can then consider whether the Defendant did or did not meet that standard of care. Expert evidence can also assist the judge or jury in establishing whether it was the negligent actions of the Defendant which caused the Plaintiff’s injury. Finally, expert evidence is often used to help the judge or jury quantify the damages of the case. This is particularly helpful in determining the cost of necessary future medical supplies, or medical care.

An example of the use of medical evidence in a medical malpractice case may be the following: a patient dies of undiagnosed cancer, despite it having been visible on previous diagnostic imaging. An expert radiologist would likely be required to give evidence as to whether or not the Cancer should have been detected on the testing which the patient underwent, whether or not it was negligent of the Defendant radiologist not to have seen and reported it. Another expert physician, possibly an oncologist, would likely be required to give evidence as to if the Cancer had been diagnosed at the time of the imaging, could the patient have been successfully treated, that is, could their life have been saved, or was the cancer too far progressed or otherwise incurable? This demonstrates the complexity of medical malpractice cases and why experts are an essential element of moving a case forward.

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