The role of the expert witness is often crucial in Australian patent litigation, especially where the invention in question is scientifically or mechanically complex. This is because a patent specification is “addressed to those likely to have a practical interest in the subject matter of [the] invention”…“with a practical knowledge and experience of the kind of work in which the invention was intended to be used.”[1] A court must, by evidence, be put in the position of a person of the kind to whom the document is addressed, being a person skilled in the relevant art at the relevant date (PSA).[2]

The PSA is a notional person who is deemed to have the common general knowledge of those working in the field to which the invention relates but who does not possess any capacity for invention. An expert witness’ role is to assist the court. If they are a PSA, they may do so, for example, by giving evidence as to how certain words in a patent would be interpreted in the relevant field, or as to the common general knowledge in the relevant field. Thus, a critical issue is whether the expert is a PSA.

In the Federal Court of Australia, in Calix Ltd v Grenof Pty Ltd [2023] FCA 378 (Calix), Justice Nicholas recently considered this very issue. His Honour’s judgement provides a timely reminder of the importance of selecting an appropriate expert witness in patent infringement proceedings, and the consequences of failing to do so.

Background to the Proceedings

Calix commenced proceedings alleging that the respondents, Grenof and Aquadex, had infringed its patent relating to a process and apparatus for the manufacture of hydroxide slurry (Patent). Grenof sought revocation of the Patent on the grounds that the invention lacked novelty, did not involve an inventive step, and did not comply with sections 40(2)(a) and 40(3) of the Patents Act 1990 (Cth) (Act). Grenof also alleged that Calix had made unjustified threats of infringement proceedings. Justice Nicholas ultimately concluded that Grenof had not infringed the Patent, that the Patent was invalid for lack of inventive step and failure to satisfy s 40(3) of the Act, and that Calix had made unjustified threats.

During the course of trial, each party provided evidence from one expert witness. Nicholas J generally preferred the evidence of Grenof’s expert witness, and stated, in quite strong terms, that Calix’s witness was not a PSA, and was unreliable, contradictory, and even stubborn.

Choosing the Right Expert Witness

The field of the invention related to the manufacture of hydroxide slurries. Calix’s expert was a professor of ceramic engineering. At trial, Grenof argued that Calix’s expert was not a PSA, and Justice Nicholas agreed. His Honour was of the opinion that Calix’s expert had very little experience, and little or no real training, in the manufacture of hydroxide slurries. In particular, his Honour was not persuaded that Calix’s expert had a practical interest in the subject matter of the Patent or that his prior training or experience qualified him to give relevant evidence. Consequently, the evidence given by Calex’s expert was given very little weight.

It is not uncommon for the admissibility of, and the weight to be given to, an expert witness’ evidence to be questioned due to a lack of specialised knowledge in the relevant field. The High Court of Australia in Dasreef Pty Ltd v Hawchar (2011) 243 CLR 588 ruled, albeit not in the context of patent infringement proceedings, that the expert evidence provided was inadmissible because it was not based wholly or substantially on the expert’s specialised knowledge, training, study or experience. Calix serves as a pertinent reminder of the importance of selecting an expert witness who is, in fact, skilled in the relevant field of the invention.

In addition to finding that Calix’s expert was not a PSA, Nicholas J found him to be unreliable, stating that the witness often provided contradictory and inconsistent evidence. Notably, his Honour criticised both the evidence provided and the witness himself because the expert “stubbornly refused to accept the obvious implication of his own evidence” and his evidence was “implausible”.

This decision is a stark reminder to current and future litigants to consider not only the expertise of potential expert witnesses, but also their reliability, demeanour and personality. The best expert witnesses speak clearly and concisely, listen carefully and answer only the questions they have been asked, and are open to changing their opinion when presented with new and clearly contradictory facts (rather than acting as an advocate or “hired gun” for the party retaining them in litigation). An expert witness’ paramount duty is always to assist the court by providing their objective and unbiased opinion.

Avoiding duplicative expert evidence

In Novartis AG v Pharmacor Pty Ltd (2022) 290 FCR 345, the Full Court of the Federal Court recently held that parties should generally only rely on evidence from one expert in any one discipline, and that if more than one expert is relied upon and the evidence is found to be duplicative and overlapping, it can be excluded.

Looking Forward

These cases serve as useful guidance for litigants. It is clear that parties (and lawyers) must choose expert witnesses carefully and with a view to the precise field of the invention, to ensure experts are appropriate avatars for the PSA, that those experts will give reliable and convincing evidence, and that, where there are multiple experts, their evidence is not duplicative. If parties fail to take these matters into consideration, they run the risk that the evidence of their expert witness may be excluded or given little or no weight by the court.