Avoid autopilot when using expert evidence
18th Feb 2021
Expert evidence is a useful tool, and having a solid understanding of expert evidence law and the common law rules is a powerful weapon for a litigator. It is a weapon that should not only be reserved for use by barristers when the hearing is imminent. Solicitors should also wield this weapon strategically and thoughtfully from the beginning of a dispute and when first considering the evidence that needs to be gathered.
Generally, opinion evidence is inadmissible unless the witness is an expert. However, rules of expert evidence have developed to prevent an expert from usurping the roles of the judge or jury.
Rules of expert evidence
The criteria for the admissibility of expert evidence can be summarised as follows:
- Expertise: the expert must have specialised knowledge based on their training, study or experience.
- Area of expertise: the specialised knowledge must be within a recognised, organised or accepted field of study.
- Common knowledge: the expert must not give evidence about matters that are within the judge’s or jurors’ own experience or knowledge.
- Basis: the facts upon which the opinion is based must be proven to the satisfaction of the court.
- Ultimate issue: the expert should not give their opinion on an ultimate fact in issue.
An opposing lawyer with a sound understanding of the rules of expert evidence will likely use these rules to attack or undermine their opponent’s experts. Solicitors should therefore thoughtfully consider the rules of expert evidence before spending their client’s money on experts.
Recent cases where expert opinion was rejected
There are several recent cases where courts have refused to admit or accept opinions of evidence due to breach of the expert evidence rules.
In Menz v Wagga Wagga Show Society Inc  NSWCA 65, the NSW Court of Appeal confirmed that the trial judge was correct in excluding the opinion of a competitive horse rider, trainer and competition judge. During the trial, the witness gave an opinion that the defendant ought to have provided more marshals and better supervision of children. She asserted that this would have prevented the children from making the loud noises that startled the horses and led to the plaintiff rider being injured. The Court of Appeal agreed that the witness did not demonstrate that she had specific expertise to comment on the management or staffing of agricultural shows.
In MacGowan v Klatt  QSC 222, during a family provision application, the Queensland Supreme Court heard evidence from two legal experts on the status of Vanuatu law regarding adoption. One of the experts gave her opinion in a manner that breached the ultimate issue rule by asserting that ‘the applicant had been adopted according to customary law, that this was to be recognised in Queensland; and that the applicant … was the legal beneficiary of the estate’ (at ). Consequently, the Court preferred the other expert.
In Hawkesbury Sports Council v Martin  NSWCA 76, the NSW Court of Appeal held that the trial judge erred in admitting the opinion of an engineer and building consultant. The witness gave an opinion on whether a pedestrian ought to have seen a steel cable strung between bollards around a sporting field. The Court of Appeal determined that the witness’s opinion on human visual perception was outside of his expertise and was a matter of common knowledge.
In Brown v Daniels  QSC 209, Davis J refused to admit the opinion of an engineer as to who caused the motor vehicle accident and held that the opinions were not based on any science. Rather the opinions were ‘simply conclusions which [were] drawn from the physical evidence’ (at ). The Court was in as good a position as the engineer to consider the evidence and draw conclusions about the movement of the vehicles at the time of the accident.
Make thoughtful and strategic decisions in regard to experts
Clients are relying on us to make sound judgements on their legal spend (including outlays). Therefore, we should not go on autopilot and enlist expert evidence unless it is warranted and likely to withstand attack from our opponent.
It is important to critically assess whether an expert is needed in the first place. We should turn our minds to the rules of expert evidence before deciding whether expert evidence is warranted.
If we have already obtained expert evidence, we should analyse the expert’s reports to check for weaknesses. Take steps to remedy defects if you detect a chink in the armour. Don't wait to hear about the defects on the first day of trial when it is too late to fix the issues or collect additional evidence.
If we fail in these steps and the expert opinion is thrown out, it will not only be embarrassing but we will also have to face a difficult conversation with our client explaining what went wrong.
However, obtaining expert evidence may have benefits even if the evidence may not withstand the rigours of attack on trial. For example, it may help with negotiations, break a deadlock, or assist a client to understand the issues. But this strategy needs to be executed carefully and should be explained to the client. This allows them to understand in advance why their legal spend is being used on experts even though the evidence may not be admissible.
We will serve our clients’ interests best if we know our expert evidence rules thoroughly and mindfully consider them every time we consider obtaining opinion evidence.
 For useful expositions of expert evidence rules, see Makita (Australia) Pty Ltd v Sprowles (2001) 52 NSWLR 705; Dasreef Pty Ltd v Hawchar (2011) 243 CLR 588; Idoport Pty Ltd v National Australian Bank Ltd  NSWSC 828.