Expert Witnesses and the Admissibility Test in Ontario

Hi Everyone, it's Kristy from Clearly Legal.

Let's chat today a bit about expert evidence.

Litigation can easily involve the need and use of experts, even simple non-complex litigation can require the use of an expert. So, expert evidence often plays a crucial role. But how do courts decide if this expert testimony is allowed? Understanding the test for admissibility of expert evidence helps to minimize the fight and question of expert evidence being admitted.

What Is Expert Evidence?

Expert evidence is testimony or information provided by someone with specialized knowledge, skill, or experience beyond that of an average person. This expert helps the court understand file facts that require expert insight. For example, an expert might explain how an elevator malfunctioned, analyze medical records, or assess structural damage to a garage door.

In Ontario, expert evidence is common in many types of cases, including personal injury, product liability, and criminal trials. The expert’s role is to clarify complex issues so the judge or jury—the trier of fact—can make informed decisions.

The Four-Part Test from R. v. Mohan

The admissibility of expert evidence in Ontario is governed by the Supreme Court of Canada’s decision in R. v. Mohan. This case sets out a clear four-part test that courts use to decide if expert evidence can be presented:

1. Relevance

   The expert evidence must be directly related to an issue in the case. It should help prove or disprove a fact that matters to the outcome.

   
   

2. Necessity

   The evidence must be necessary to assist the trier of fact. This means the expert’s knowledge should provide insight beyond what a typical person could understand.

   
   

3. Absence of Any Exclusionary Rule

   The evidence must not be excluded by any legal rule.

   
   

4. Proper Qualifications

   The person providing the expert evidence must have the right credentials, experience, or training to be considered an expert in the relevant field.

   
   

Each part of this test ensures that expert evidence is both useful and reliable.

Expert evidence plays a vital role in Ontario legal cases by providing specialized knowledge that helps the trier of fact understand complex issues. The R. v. Mohan four-part test ensures that only relevant, necessary, properly qualified evidence is admitted. Knowing this test helps you evaluate and prepare expert testimony effectively.

How a Law Clerk can help

Imagine you are looking at an appeal where someone was wrongfully convicted based on the use of the R. v. Mohan test. You would want to review testimony, file evidence and pleadings. I can help; in fact, I helped with this precise project last year. Contact me at kristy@clearlylegal.ca and we'll chat about how I can help review for your appeal.