Expert Evidence and the Judge as Gatekeeper

January 26, 2015 | Kate Genest

For expert evidence to be admissible, it must be: (a) relevant; (b) necessary to assist the trier of fact; (c) it must not be subject to any exclusionary rules; and (d) the expert must be properly qualified (R. v. Mohan).

Earlier this month, in Meady v. Greyhound Canada Transportation Corp., the Ontario Court of Appeal examined a trial judge’s decision to exclude expert evidence for failing to meet the second requirement of necessity. The Court of Appeal ultimately upheld the trial judge’s decision and noted in its reasons that there has been a growing recognition of the responsibility of the trial judge to exercise a more robust “gatekeeper” role in the admission of expert evidence.

The case arose from a sad set of facts. 21-year old Shaun Davis was on a bus trip from Calgary to spend Christmas with his family in Pictou, Nova Scotia. On a leg of the journey in northern Ontario, Davis left his seat at the front of the bus, ignored the driver’s requests that he return to his seat, then, suddenly, lunged at the driver and grabbed the steering wheel. The bus veered off the road and toppled on its side. One person was killed and many of the 32 passengers were injured.

A number of passengers sued Greyhound and the bus driver, the two OPP officers who had contact with Davis before he boarded the bus, and their employer, Her Majesty the Queen in Right of Ontario. They also sued Davis.

After a trial lasting more than 60 days, the trial judge dismissed the action against all defendants, other than Davis.

The trial judge rejected the argument that the officers should have detained Davis or that the OPP did not adequately train the officers to respond to people with mental illness. The trial judge also found the appellants had not established that the driver failed to exercise reasonable care and skill in the operation of the bus or that Greyhound had failed to properly train him. The driver had no reason to anticipate that Davis would act as he did.

 The plaintiffs appealed on the basis that the trial judge erred by excluding the evidence of two expert witnesses, one a specialist in police training and the other an expert in bus safety.

 The specialist in police training was going to offer the opinion that the police officer failed to meet the standard of care of a reasonable and prudent police officer by failing to follow police practices. The trial judge concluded that he did not require expert opinion in this case. He observed that the police policies and procedures could be adduced in evidence and that the officers could be cross-examined on their compliance.

 The expert in bus safety had experience as an accident investigator and in drafting policies and standards for training bus operators. The trial judge found that the bus safety expert’s opinion was also not necessary: expert evidence was not needed to determine what the driver knew or ought to have known regarding his duties as an operator, nor to determine the appropriate speed of the bus in relation to road conditions, the steps that the driver should have taken when Davis came to the front of the bus, how he ought to have reacted to Davis grabbing the wheel, or what other steps he ought to have taken to avoid the accident.

The appeal was dismissed. Expert evidence is only necessary where subject matter of the inquiry is outside of the normal experience of a judge or jury. There is, however, no bright line between what is and what is not within the normal experience of the trier of fact, and for this reason, the Court of Appeal affirmed that much deference is owed to the exercise of the trial judge’s gatekeeper function. In this case, the Court of Appeal found that the trial judge properly exercised that function.


This blog sets out a variety of materials relating to the law to be used for educational and non-commercial purposes only; the author(s) of this blog do not intend the blog to be a source of legal advice. Please retain and seek the advice of a lawyer and use your own good judgement before choosing to act on any information included in the blog. If you choose to rely on the materials, you do so entirely at your own risk.