Qualifying expert witnesses in the Tax Court of Canada | Yao v. The Queen

7 minute read
12 May 2022

Yao v. The Queen[1] affords a practical overview of how the Tax Court of Canada ("TCC") determines admissibility of proposed expert evidence. This article discusses the TCC's approach in that case and highlights some practical considerations for expert evidence in TCC appeals.

Framework for admissibility

The TCC in Yao held a voir dire, which is a motion or mini-hearing, where the proposed expert witnesses can be questioned on issues relevant to admissibility. As a framework for determining admissibility, the TCC applied the two-part test:

  1. threshold admissibility; and
  2. the gatekeeper function or the residual discretion to exclude.

In determining threshold admissibility, the TCC applied a four-part test.

The first part of this test is to consider whether the proposed expert evidence is logically relevant. Relevancy in this context is a low hurdle determined by reference to the issues, as framed in the pleadings (notice of appeal, reply and answer, if any). Essentially, the question to be addressed is whether the proposed expert evidence makes the existence or non-existence of a fact in issue more or less likely than it would be without that evidence.

The second part of the test is to consider whether the proposed expert evidence is necessary to assist the trier of fact. The focus here is on enabling the TCC to appreciate technical matters in issue. Many cases have illustrated this factor as providing the Judge with "prescription glasses," through which technical information may be viewed before being analyzed and weighed by the Judge.

The third and fourth parts of the test are to consider whether there are any applicable exclusionary rules and whether the proposed expert is properly qualified or has the requisite credentials.

In applying the second part of the test, or the gatekeeper function, the TCC engages in a cost-benefit analysis, comparing the help versus the harm of the evidence. Put another way, the TCC considers whether the probative value of the proposed expert evidence outweighs the potential prejudice, confusion and prolonged Court time that would result if it were to be admitted.

If the proposed expert evidence passes both parts of the test and gets admitted, the TCC ultimately decides how much weight to give it, considering its probative value.

Application in Yao

The issue for the TCC in Yao was whether the appellants, as refugee claimants, were "temporary residents" (under Income Tax Act section 122.6) and thereby qualified for the Canada Child Tax Benefit. The Minister had determined that refugee claimants were not temporary residents, thus giving rise to this issue. An alternate ground for appeal was that the Minister's determination, even if it was otherwise legally correct, infringed the appellants' constitutional rights under sections 7 and 15 of the Canadian Charter of Rights and Freedoms ("Charter").

The appellants proposed three expert witnesses:

  1. a sociologist
  2. a psychologist; and
  3. an immigration lawyer

The evidence for the first two proposed expert witnesses, the sociologist and the psychologist, was admitted by the TCC . The determination of this issue was relatively clear, in that social science evidence like this can be materially important in cases involving Charter issues.

The TCC arrived at the opposite conclusion, however, for the immigration lawyer. Her proposed expert evidence was excluded. In deciding whether to admit her evidence, her proposed expert report was conceptually considered in two parts:

  1. the legislative history and context concerning various statutes; and
  2. observations on wait times, durations and pathways for refugee determination.

The TCC pointed out that it is trite law that legal opinion testimony on domestic law is inadmissible. Moreover, the TCC considered the overall probative value of the proposed expert evidence to be low, relative to the time and cost that would be incurred, especially for evidence on topics that were already going to be covered by other testimony.

The TCC explained that the proposed expert report "… read like a usual written submission the Court is likely to receive at the conclusion of this trial" and that "… if [the proposed expert] appears before the Court because of her superlative knowledge in an area of domestic immigration law, she may do so as a lawyer from the lectern beside the counsel table and not as an expert in the witness box."

Practical considerations of expert evidence in the TCC

Expert witnesses always need to be seen to be impartial, independent and objective. All communications between the expert and counsel for the party who retained the expert must accordingly support this foundational aspect of the expert's role. It can be seriously prejudicial if the expert is instead perceived to be merely an advocate or gladiator for one of the parties. The weight ascribed to their evidence could be materially diminished or their evidence could be excluded.

In the right case, expert evidence can be extremely helpful to support timely settlement negotiations. Providing Department of Justice counsel with expert reports, at least in draft, at the pleadings stage, can be instrumental in negotiating reasonable settlements early in the process.

Employees of a corporate appellant with first hand knowledge of the facts in issue, who also have subject matter expertise, can be considered by the TCC as litigant experts eligible to provide expert evidence. This allows the scope of proper questioning for litigant experts to effectively be expanded beyond first hand knowledge testimony to providing opinions.

As illustrated in Yao, challenges can arise when an expert is proposed on the basis of their knowledge of the practical operation of a regime. This can give rise to issues relating to both relevance and probative value.


Potential expert evidence in TCC appeals must always be approached carefully, in its preparation and optimal utilization throughout the process, as well as seeking to have it admitted in the TCC. While it can be instrumental in successfully resolving tax disputes, there are also pitfalls to be avoided.

Should you have any specific questions about this article or would like to discuss it further, you can contact the author or a member of our Tax Dispute Resolution Group.

[1] 2022 TCC 23 ("Yao")

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