In R v. Mohan, [1994] 2 SCR 9 the Supreme Court of Canada (the “SCC”) noted that expert witnesses can distort the fact-finding process and lead judges to give more weight to their evidence than is deserved. The SCC also noted that the benefits of an expert witness’s evidence must be weighed against the costs of receiving it – which can be very high – and the risks of admitting it, which includes the risk of admitting junk science into the record or ending up in a contest of experts. However, expert evidence often provides information that the Court requires to make a just ruling in a technical case.

The Tax Court of Canada (the “TCC”) has begun to utilize two particularly interesting techniques for trials where multiple completing expert witnesses are expected to be heard. Hearing expert witnesses concurrently – as opposed to the parties calling their expert witnesses one by one  – and through “hot tubbing” expert witnesses.

Calling expert witnesses concurrently was a practice that the TCC introduced in 2014. In 2019, the TCC built on this practice by introducing “hot tubbing”, wherein the parties file their expert reports prior to trial, and then the judge convenes an expert panel at the pre-trial stage.¹ This allows one judge to oversee the pretrial expert panel, with another judge preparing the questions for the hearing.² The experts are then concurrently examined at the trial or hearing, although there are limits imposed on cross-examining experts during the trial, which is a departure from how hot tubbing is implemented in other jurisdictions.³ Discussion of how “hot tubbing” differs between jurisdictions can be found elsewhere. After the judge questions the expert witnesses at trial, counsel may then cross-examine only to clarify and expand on the answers already given or to raise entirely new questions based on the matters that the experts raised in their previous answers.⁴

Overall, hot tubbing shifts the control of expert evidence from counsel to the judge, hopefully resulting in less partial expert evidence being given. Trusts and Estate disputes often require expert evidence, and competing experts are a routing aspect of these hearings. However, the cost of hiring several experts, undergoing the process of introducing them into the hearing, and cross-examining them thoroughly can be a time-consuming and costly endeavour. It can also result in a contest of experts, with each expert giving partial evidence, which can result in confusion for the trier of fact. The routine need for expert evidence in Trust and Estate disputes makes this area one that could greatly benefit from the use of “hot tubbing” and the concurrent examination of expert witnesses.

1. Canadian Lawyer, “Hot-tubbing experts — should lawyers like it?” (04 July 2011), online: Canadian Lawyer < https://www.canadianlawyermag.com/practice-areas/litigation/hot-tubbing-experts-should-lawyers-like-it/268255>; and Sam McDonald, “’Hot Tubbing’ of Expert Witnesses: Experiences in Other Jurisdictions and Expected Issues at the Tax Court of Canada” (2023) 71 Canadian Tax Journal 985 at pages 986-987. ↩︎
2. Ibid. ↩︎
3. Ibid. ↩︎
4. Ibid. ↩︎