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The Role of an Expert in Professional Negligence Claims

The authors of this blog are Peter Weissman and David Wagner .

Liability in negligence does not necessarily follow where the conduct of one person has caused economic loss to another. To impose liability, you must first establish the existence of a duty of care and a failure on the part of the defendant to meet the required standard of care.1

Presuming that a duty of care exists, the Court must determine the appropriate standard of care,2 which clarifies the extent of the duty.3 In negligence, the standard of care is that of a reasonable person in similar circumstances.4

Expert evidence is often used to help establish the parameters of the standard of care owed. However, in certain types of cases, such as professional negligence, the use of expert evidence is mandatory subject to the following narrow objections:5

  1. Cases in which it is possible to reliably determine the standard of care without the assistance of expert evidence. “This will be the case only where the court is faced with ‘nontechnical matters of those of which an ordinary person may be expected to have knowledge’”; and
  2. Cases in which the impugned actions of the defendant are so egregious that it is obvious that his or her conduct has fallen short of the standard of care, even without knowing precisely the parameters of that standard

For example, expert evidence will be necessary to establish what another reasonably skilled and experienced professional would have done where the plaintiff is suing his former tax advisors for professional negligence.6 In contrast, where the plaintiff’s claim focuses on damages flowing from an accounting missing a filing deadline, expert evidence will not be necessary.7

Where expert evidence is necessary, it is imperative that the proposed expert be properly qualified to opine on the matters at issue.

To qualify, an expert witness must be shown to have acquired special or peculiar knowledge through experience or study in respect of the matter on which s/he will testify.8 If, however, “the witness’s ‘special’ or ‘peculiar’ knowledge on a subject matter is minimal, he or she should not be qualified as an expert with respect to that subject”.9

In certain cases, it is not difficult to satisfy this criterion. For example, where a geriatric psychiatrist or certified capacity assessor opines on an individual’s capacity to appoint a power of attorney. Certain fields have measures which avoid this uncertainty and subjectivity. For example, the law society of Ontario certifies lawyers as specialists in particular fields, which provides an easy avenue to determine if a proposed expert is sufficiently qualified.10

However, in other scenarios, ensuring that the proposed expert is sufficiently qualified can be difficult. For example, CPA Ontario, the regulatory body for accountants in Ontario and its cohorts in the other provinces and territories, do not offer similar types of certifications for tax accountants. Most tax accountants in Canada have completed (or are in the process of completing) CPA Canada’s In-Depth tax course and/or The University of Waterloo’s Masters of Taxation Program. The Trust and Estate Practitioner (TEP) designation provided by the Society of Trust and Estate Practitioners of Canada is an identifiable designation that some tax practitioners possess, but it neither covers the whole range of tax services nor is limited to accountants.

To determine whether an expert is appropriately qualified, the lawyer must accurately identify the general issue on which the expert is being asked to opine. It is then preferable that the expert also has ‘special’ or ‘peculiar’ knowledge of how the general issue applies to the unique and nuanced factors of the particular case.11

The purpose of expert evidence is to assist the trier of fact by providing insight that the average trier of fact does not already have. Where expert evidence is necessary, it is imperative that the lawyer consult with and produce an expert witness who is appropriately qualified to opine on the matters at issue in that particular case.

While defining the appropriate standard of care in professional negligence claims will ultimately be a question of law,12 the Court will generally require expert evidence to define the precise parameters of the standard of care and determine whether those standards have been breached.13 The success of such claims depends heavily on a properly qualified expert opinion.

  1.   Garratt v. Orillia Power Distribution Corp., 2008 ONCA 422 at paras. 36-37
  2.   Donoghue v. Stevenson (1932) UKHL 100, (1932) AC 562 at 620-621
  3.   Ryan v. Victoria (City), (1999) 1 SCR 201, 1999 CarswellBC 79 at para. 21
  4.   Hill v. Hamilton-Wentworth (Regional Municipality) Police Services Board, 2007 SCC 41
  5.   Krawchuk v. Scherbak, 2011 ONCA 352 at paras. 132-135
  6.   Bari v. Ahuja, 2018 ONSC 5726 at para. 65; Vernon v. NEO Family and Children’s Services, 2018 ONSC 7231 at para. 6
  7.   Dyck v. F.M.A. Farm Management Associates Ltd., 1996 CanLII 6766 (SK QB), 1996 CarswellSask 14
  8.   Mohan, Supra note 20 at para. 27
  9.   R. v. K. (A.), Supra note 42 at para. 103
  10.   Law Society of Ontario. (2019), online:
  11.   See R. v. Amara, 2010 ONSC 251 at para. 44. In contrast, in Imeson v. Maryvale (Maryvale Adolescent and Family Services), 2018 ONCA 888 at paras. 86-90 (Imeson), the Ontario Court of Appeal disqualified the expert who had the qualifications of a mental health clinician, but did not demonstrate that he had specific expertise in sexual abuse.
  12.   Kripps v. Touche Ross & Co., 1997 CanLII 2007 (BC CA), 1997 CarswellBC 925 at para. 70; Canadian National Railway v. Vincent, (1979) 1 S.C.R. 364, 1978 CanLII 166, 1978 CarswellQue 137 at para. 22
  13.   Alfano v. Piersanti, 2012 ONCA 297 at para. 104

The authors of this blog are Peter Weissman and David Wagner .

Peter is and partner at Cadesky Tax in Toronto. David is a member of the firm’s Estate and Commercial Litigation Groups. He received his TEP designation from STEP and he deals with will challenges, dependants support, guardianship and applications to compel an accounting.

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This blog is not intended to serve as a comprehensive treatment of the topic. It is not meant to be legal advice. Every case turns on its specific facts and it would be a mistake for the reader of this blog to conclude how it might impact on the reader’s case. Nothing replaces retaining a qualified, competent lawyer, well versed in this niche area of practice and getting some good legal advice.
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