Litigation 101: Expert witnesses in a civil proceedings: practical tips

This article provides practical tips for briefing an expert in civil proceedings. While the exercise is nuanced, case-dependent and jurisdiction-specific, understanding the key ethical, evidential and strategic considerations helps to avoid missteps which may not become apparent until trial.

What is the role of an expert witness?

Expert witnesses give opinion evidence, often in relation to complex subject matter, in a proceeding. The purpose of expert evidence is to provide the court with an objective and impartial assessment of an issue from a witness with specialised knowledge based on the person’s training, study or experience. The opinion must be wholly or substantially based on the witness’ expert knowledge and the facts relied upon must be identified and proved.

Generally, opposing parties in a proceeding will retain an expert witness within the same field to each prepare a report on the relevant subject matter. In some jurisdictions, courts will generally order experts to prepare a joint report following a conclave conferral process (in the absence of the parties and their lawyers), identifying any areas of agreement and disagreement (and the reasons for any areas of disagreement). Courts may also order that the experts give their evidence during any trial concurrently, colloquially known as an expert evidence “hot tub”.

Independence of expert witness

A key takeaway from this article should be that an expert witness is not a “hired gun” or an advocate for a party. They have a paramount duty, which overrides any duty to the party who has retained them, to assist the court impartially on matters relevant to their area of expertise.

Parties must bear this in mind at all times in dealing with their expert. Any actual or perceived compromise of this principle runs the very real risk of a court ruling that some or all of the expert’s evidence is inadmissible. A failure to maintain the proper independence expected of an expert witness initially had catastrophic consequences for one party’s case in New Aim Pty Ltd v Leung [2022] FCA 722. While the Full Federal Court recently disagreed with the primary judge's rejection of the entirety of the expert witness' evidence (New Aim Pty Ltd v Leung [2023] FCAFC 67), the Full Court reiterated the need to maintain the independence of an expert witness and transparency in the process.

Cogent expert evidence and the role of legal representatives

For the opinions of an expert to have any value, the evidence must clearly identify all material facts and/or assumptions upon which the opinion is based. No weight will be given to the evidence if the underlying factual basis is not made out. As Justice Jackson explained in Peebles v WorkCover Queensland [2020] QSC 106.

“One of the critical requirements of a persuasive expert report is that it clearly identifies the factual assumptions on which the opinions expressed are based. It is only when the assumptions are identified that the foundation of the opinion can be seen and the corresponding strength of the opinion assessed.”

It follows that all relevant facts must be given to the expert, not just one party’s version of events. If this is not done then the expert evidence may be worthless or even counter-productive.

Relatedly, courts have provided guidance on the tasks which can (and depending on the circumstances, should) be properly performed by legal representatives in preparation of an expert report. These include:

• organising the evidence so that it is presented in a way that is accessible, comprehensible and does not contain irrelevant material;
• ensuring that experts identify their chain of reasoning and factual assumptions underpinning the independent opinions expressed by an expert;
• addressing issues of admissibility, and identifying any obscurities and gaps in an expert’s reasoning; and
• testing an expert’s reasoning process.

In performing those tasks, the primary ethical consideration must always be to ensure that the independence of an expert’s evidence is not, and cannot be perceived to be, compromised by the legal representatives.

Legal professional privilege and expert reports

Legal professional privilege (LPP) protects certain communications from disclosure. At common law, it will apply to confidential communications created or prepared in anticipation of or during pending litigation for the dominant purpose of the litigation (eg. with a view to obtaining legal advice or evidence for use in the litigation).

The principles of LPP insofar as expert reports, drafts and communications with experts are concerned can vary. They may depend on jurisdiction, whether the particular situation is governed by the common law or the relevant jurisdiction’s evidence legislation, the context in which documents are sought and the particular circumstances in which the documents came into existence. As a general guide, however, some oft-cited guidance in respect of particular documents include:

1. confidential brief or instructions to expert: privileged;
2. copies of documents (where copies made for purpose of confidential communications between lawyers and expert witness): privileged;
3. expert’s working notes, field notes and drafts of reports, if prepared for purpose of witness developing their own opinion: not privileged (because they would not expose communications with a lawyer).

It is important to note that disclosure of the expert’s report for use in litigation will ordinarily result in an implied waiver of LPP documents (ie. 1 2 and 3 above). This will apply where the documents are used in a way that influences the content of the report because it would be unfair to rely on the report without disclosure of the documents.