Evidence Based Expert Testimony

David Debenham, McMillan LLP

In  R. v. Millard,  (“Millard”), an Ontario court explained the concept of “evidence based” expert testimony, an emerging nuance on the traditional tests for the admissibility of expert evidence, no matter what the court, and no matter what the subject matter of the testimony.  Put briefly, experts will no longer be able to put on their white laboratory coat and ask courts to accept their methodologies and underlying data on faith:  The process will now be one that requires the expert to disclose the basis of their opinions, the data upon which it relies, and the inherent weaknesses or limitations in their approach.  Transparency is now the watchword.  No longer can the expert show up with an impressive resume and expect the trier of fact to take the expert’s methodology as sound, and data as accurate, because it is too complicated and time consuming to explain their underlying analysis to a judge and jury.  We are going from a world of “trust me” to one of “show me”. 

In Millard, the accused was charged with the first degree murder of his father, who died as the result of a gunshot wound to his left eye. The central issue is whether the gunshot was the result of suicide, or murder.   The Crown sought to introduce expert evidence in the area of “Shooting Scene Reconstruction”.  The court held that only the evidence of the general operation of revolvers and the evidence of the specific design and operation of the revolver in this case was admissible.  The balance of the expert’s opinion with respect to the position, orientation and location of the gun when discharged and the likelihood that the deceased discharged the shot given his body position was ruled inadmissible.  This result is unremarkable.  The analysis to get to that result is.

The court started with the standard analysis:

  1. Opinion evidence is presumptively inadmissible and the party seeking to introduce it bears the onus of establishing its admissibility on the balance of probabilities.
  2. Expert evidence is admissible when it is
    1. relevant,
    2. necessary to assist the trier of fact;
    3. not subject to any other exclusionary rule;
    4. the expert is properly qualified, which includes the requirement that the expert be willing and able to fulfil the expert’s duty to the court to provide evidence that is:
      1. Impartial,
      2. Independent, and
      3. Unbiased.
  3. For opinions based on novel or contested science or science used for a novel purpose, the underlying science must be reliable for that purpose, and
  4. The trial judge, in a gatekeeper role, determines that the benefits of admitting the evidence outweigh its potential risks, considering such factors as:
    1. Legal relevance,
    2. Necessity,
    3. Reliability, and
    4. Absence of bias.

So far, no surprises.  The challenge to the admissibility of the proposed expert in this case did not raise any additional exclusionary rule, nor was the science said to be novel.  That is usually the case.  What is unusual is to go on to acknowledge the dangers of expert testimony, recognizing that there is a temptation to simply defer to an expert and rely on their testimony rather than going to the trouble to understand it, and with that understanding, grasp its limits and weaknesses.  Opposing counsel, lacking the expertise “may be hard-pressed to perform effectively their function of probing and testing and challenging evidence because its subject matter will often pull them beyond their competence, let alone their expertise. This leaves the trier of fact without sufficient information to assess its reliability adequately, increasing the risk that the expert opinion will simply be accepted.  The court then recognizes that the real question in every case becomes: “When should we place the legal system and the truth at such risk by allowing expert evidence?”   The answer is “Only when lay persons are apt to come to a wrong conclusion without expert assistance, or where access to important information will be lost unless we borrow from the learning of experts. …it is not enough that the expert evidence be helpful before we will be prepared to run these risks. That sets too low a standard. It must be necessary.”

The court then goes on to explain the new “show me” , or “evidence based” approach.  The four conditions are:  

  1. the theory or technique used by the expert must be reliable, and so too must the use of that theory or technique by the expert;
  2. the expert must not be biased;
  3. the expert must be objective and complete in collecting evidence, must reject all information that is not germane to the theory or technique being used, and must be transparent about all information and influences they have been exposed to; and
  4. the expert must clearly express not only the opinion, but also the complete reasoning process that led to it, and must be candid about the shortcomings of the theory or technique employed and the opinion reached, offering fair guidance on the level of confidence that can be placed in the opinion expressed.

An expert must now demonstrate an ‘open mind to a broad range of possibilities’.  Several forms of bias can often be unconscious: 

  1. Lack of independence bias (because of a connection to the party calling the expert);
  2. ‘adversarial’ or ‘selection’ bias (where the witness has been selected to fit the needs of the litigant); 
  3. ‘association bias’ (the natural bias to do something serviceable for those who employ or remunerate you); 
  4. professional credibility bias (where an expert has a professional interest in maintaining their own credibility after having taken a position);
  5. ‘noble cause distortion’ (the belief that a particular outcome is the right one to achieve); and, a related form of bias, ‘confirmation bias’ (the phenomenon that when a person is attracted to a particular outcome, there is a tendency to search for evidence that supports the desired conclusion or to interpret the evidence in a way that supports it). 

In this case, the expert’s opinion was premised on there being no intermediary surface to block the deposit of gunshot residue on the deceased, proving it must have been murder.    In this case, the expert was aware of a photograph showing a blanket that must have been moved from the area of the head of the deceased.  This blanket could have been an intermediary surface.  The expert did not disclose the possibility of the blanket as an intermediary surface. The expert failed entirely to disclose the evidence of the blanket or his reasoning process in relation to it, in his notes, report or testimony-in-chief.  Indeed the expert testified that, based on the photographs, there had been no movement of items at the scene and therefore no presence of an intermediary surface.    Once confronted with the photograph, the expert then explained in detail why the movement of the blanket made no difference to his ultimate conclusion.  The court found that the photograph was a significant piece of evidence that could impact adversely on the conclusions he reached, and the expert’s explanation demonstrated confirmation bias.  The court ruled that: “He was unwilling or unable to interpret this evidence in a way that was inconsistent with his theory.”  The court also noted that: “Confirmation bias is closely related to tunnel vision which has been defined as ‘the single-minded and overly narrow focus on a particular investigative or prosecutorial theory, so as to unreasonably colour the evaluation of information received and one’s conduct in relation to that information.’”  Even more damning, the judge found that “the failure of a proposed expert to disclose information that would undermine his opinion goes beyond confirmation bias.  … the expert witness’s “failure to disclose demonstrates a misapprehension of his role as an independent, neutral scientist.  A scientist is not entitled to discount a potential defence position (or indeed a Crown position) and then fail to disclose evidence which might bear upon that position… He was not entitled to discount the theory that an intermediary surface was implicated without disclosing evidence that might bear upon that theory.”

What does this all mean?  

First, an expert report should cite authorities demonstrating that:

  1. the approach or methodology used is “textbook”, meaning that it is widely accepted in the profession, and
  2. it is being applied in a traditional way. 

If this cannot be done, the report must disclose the novelty of the method, or the novelty of its application to the evidence at hand. 

Second, the expert’s report must disclose all of the relevant evidence, whether its was relied upon, discounted, or dismissed, and why.  Relevance in this context must be given a broad definition, as the court is the ultimate arbiter of relevance.

Third, the expert’s report must set forth how the methodology was applied to sift through the evidence to come to the conclusion reached, and the importance of the various constituent elements to the foundation of the opinion itself.  For example, if fact X is found to be untrue, then conclusion Y must change. 

Finally, the expert’s testimony must follow from his or her report, and both must be predicated on the accepted wisdom of their profession, and not the personal opinions of the expert dressed in the technical language of the profession.  This includes the scope of the opinion, as well as its contents.