The Role of Expert Witnesses: Under Review

A recent High Court decision has reaffirmed the principle that expert witnesses should only give opinion evidence strictly in the area(s) of their expertise.

Expert Witness Criticism

The court was particularly critical of one expert witness in the recent case of B v Minister for Education & Ors [2024] IEHC 313.

Mr. Justice Simons stated that the extent of her evidence “went far beyond that permitted by the rules in relation to expert evidence”. The independence of that expert witness was thus undermined and the court could attach little weight to her evidence.

Expert Evidence Principles

The court usefully re-stated the following principles relating to expert evidence as set down by the Court of Appeal in Duffy v McGee [2022] IECA 254:

• An expert witness is there to assist the court, not to decide the case.
• The court has no obligation to accept the evidence of any particular expert, even if that evidence is uncontradicted.
• The duty of an expert witness to assist the court overrides any obligation to any party paying the fee of the expert witness.
• An expert witness should state the facts or assumptions upon which his or her opinion is based and should not omit to consider material facts which could detract from their concluded opinion.
• An expert witness should offer independent assistance by way of objective, unbiased opinion in relation to matters within their expertise.
• An expert witness should never assume the role of an advocate.

In the case of Duffy v McGee, Mr. Justice Noonan observed that: “objectivity, by definition, requires that one has regard to both sides of the case. A central component of the duty of the expert is to ascertain all relevant facts, whether they support the client’s case or not”.

Conclusion

Parties instructing expert witnesses in litigation must be clear as to their role and duties to ensure that the evidence given is limited strictly to their area(s) of expertise.

It is clear from recent decisions of the superior courts that the expression of opinion outside an expert witness’ area(s) of expertise may be fatal as the court may be justified in attaching little weight to their evidence.

Further Information

For further advice on Commercial Litigation matters, please contact Ciarán Leavy, Partner and Head of the Commercial Litigation & Dispute Resolution Team.