Expert Reports and the New Rules of Court: The "Factual Assumptions" Requirement
One of the requirements in the new BC Supreme Court Rules is for expert reports to clearly set out the “factual assumptions on which the opinion is based“. Failure to do so could result in a report being excluded from evidence. Reasons for judgement were released this week by the BC Supreme Court, Vancouver Registry, addressing this requirement.
In this week’s case (Knight v. Li) the Plaintiff attempted to cross 41st Avenue in Vancouver, BC when his vehicle was T-boned by a the Defendant. The Plaintiff had a stop sign and was the ‘servient driver’. The Defendant was speeding. Mr. Justice Harris found the Plaintiff 75% at fault for the crash and the Defendant 25% at fault. The reasons for judgement are worth reviewing in full for the Court’s through discussion of the legal principles at play in intersection crashes.
In the course of the lawsuit the Plaintiff introduced an expert report from an engineer. The Defendant objected to the report arguing that it did not comply with the rules of Court. Mr. Justice Harris ultimately did allow the report into evidence but made the following critical comments addressing an experts need to clearly set out the factual assumptions underpinning their opinions:
 Our new Supreme Court Civil Rules codify the obligations of experts testifying in our Court. In my view, they restate obligations our law has long recognised. The Civil Rules require a clear statement of the facts and assumptions on which a report is based. It was incumbent on Mr. Gough to state clearly the assumptions on which his report was based. He did not do so. He did not provide me with an opinion of the effect of Mr. Li’s excessive speed on his ability to avoid the collision as he claimed. He gave me an opinion of Mr. Li’s ability to avoid the collision if certain assumptions favourable to Mr. Knight were made. He said nothing about being instructed to make those assumptions and nothing about the effect on Mr. Li’s ability to avoid the Accident if those assumptions did not hold.
 It must be remembered that Mr. Gough’s report is his evidence. In my view, the report as written did not comply with the requirements in the Civil Rules to state the facts and assumptions on which it is based. There is nothing improper in an expert accepting assumptions of fact that affect the opinions the expert provides, but they must be clearly stated. If they are not, there is a real risk that the trier of fact could be misled. In this case it required cross-examination to demonstrate the implications of the assumptions for the conclusions reached about Mr. Li’s ability to avoid the Accident. In my view, in this case, given the opinion being offered, the report should have clarified the effect of the assumptions about Mr. Knight’s driving on the conclusions about Mr. Li’s ability to avoid the Accident. By failing to do so, this aspect of the report descended into little more than a piece of advocacy.