A doctor’s guide to being an expert witness

DURING a trial, witnesses give evidence orally in court. They are examined and cross-examined. Many find it both a nerve-wracking and frustrating experience. In this article, we will consider why we need experts to give evidence, what barristers are trying to do when they cross-examine, and how to prepare for giving evidence.

Why experts in court?

The law, as well as common sense, distinguishes between “common knowledge” and “specialised knowledge”. We need experts both to describe things (eg, surgical technique and pathology) that are beyond the scope of common knowledge and to interpret the findings of investigations conducted with the advantage of specialised training and experience.

For expert witnesses’ opinions to be admissible in evidence, the witnesses must be qualified in a field of specialised knowledge; their knowledge must be based on training, study or experience (or a combination of them); and their opinions must be based “wholly or substantially” on the expert’s specialist knowledge (Section 79).

The expert’s role can involve conducting investigations that require specialised knowledge, presenting the findings, and offering conclusions to be drawn from those findings. Another role of experts can be to offer a critique of investigations conducted by others and the conclusions to be drawn. Many trials are conducted, in effect, as contests between experts.

This can lead to partisanship on the part of experts and consequent criticism by judges. For an expert to be criticised by judges is both a demoralising experience and a reputational blow, which can be avoided by preparing carefully for court. The first step in that preparation is to understand the limits of expert evidence.

What are the limits of expert evidence?

First, experts must bring independent minds to the case no matter who requests their opinions. Experts are not advocates for one side or the other.

Second, they must not stray outside their field of expertise.

Third, just being an expert is not enough. Experts must be able to explain the basis of their conclusions. The expert must be able to state what evidence and assumed facts led to the conclusion and how that conclusion was reached. Speculation and views based on generalities are inadmissible.

In HG v The Queen, a child sexual assault case, Chief Justice Murray Gleeson criticised a child psychologist who gave evidence for the defence in the trial. It is a stern warning. He said (among other things):

“It is important that the opinions of expert witnesses be confined, in accordance with s 79, to opinions which are wholly or substantially based on their specialised knowledge. Experts who venture ‘opinions’, (sometimes merely their own inference of fact), outside their field of specialised knowledge may invest those opinions with a spurious appearance of authority, and legitimate processes of fact-finding may be subverted.”

What are advocates trying to do?

Good barristers go into a trial with a theory of their case, and a plan for persuading the court to accept that theory. The theory will be based on the evidence they have available, their client’s version of events, other information provided by the client, the law and their knowledge of the world and human beings. This leads to a final address that is intended to persuade the court to accept their theory and to reject the alternative theory.

When an advocate calls a witness, the examination of that witness is called “examination-in-chief”. One of the main rules of practice is that the examiner must not ask leading questions about disputed issues. On contentious issues, open questions must be asked.

The examination-in-chief is generally based on a witness statement or expert report prepared some time before the trial. If you are to be called as a witness, your report will be given to the other side. It should therefore be written with that in mind. It is important that the report be objective, clinical and reasonable and be based only on facts and facts you have been asked to assume (as well as, of course, your training, study and experience). The report should not make speculative observations or personal remarks that have no clinical significance.

In preparing their reports, experts usually rely on documents such as patient records and other records created contemporaneously with the events about which the report is being given. Those contemporaneous records can be used to refresh the witness’ memory both when writing a report and also in court. Experts are usually allowed to refer to their reports while giving evidence, but may not have direct access to the original records on which the report is based. When necessary, they will be shown the records or they can ask for access to them. If an expert witness needs to see the records to answer a question, they should say so. The judge will usually allow this.

What is cross-examination?

Cross-examination is a method by which the oral evidence of a witness is tested. The two main purposes of cross-examination are to obtain evidence favourable to the cross-examiner’s client or to undermine the witness’ evidence. Cross-examiners may have both purposes in mind when they cross-examine.

Favourable evidence given by the opponent’s witnesses is more powerful than self-serving evidence. Therefore, good defence counsel often seeks to cross-examine the other side’s witnesses to obtain useful concessions from them.

Ideally, cross-examination should not be conducted crossly. Judges dislike overbearing advocates attempting to bully witnesses. The honest indignation of the witness standing up to being bullied tends to enhance their credibility in the eyes of the court and to diminish the standing of the advocate.

Techniques used by counsel to cross-examine expert witnesses include the following:

• testing the bases of the expert report – the facts and assumed facts on which the expert relies may be in contention. “An expert opinion is only as persuasive as the facts upon which it is based”;
• attacking the quality of the investigations or the competence of the witness;
• eliciting concessions;
• confining the opinion within narrow limits. Cross-examiners will sometimes try to demand “yes” or “no” answers – there is no rule of law that they can do so; witnesses must answer relevantly and responsively to the question; and
• suggesting that the expert is partial or biased rather than truly independent.

How to prepare for court

Lawyers are not permitted to coach witnesses or put words in their mouths. They can, however, prepare witnesses for the experience of giving evidence. At the pre-trial meeting, the lawyers will go through your report with you and ask you questions about it. They can ask you about any problems they see in the evidence, such as inconsistencies. They can also inform you about the general issues that are likely to arise in the trial and the matters about which you may be cross-examined. If the discussions lead to new questions, they may ask you for a supplementary report.

Here are some further tips:

• if you have not been to court before, visit a court to get a feel for the layout and ambience;
• close to the time of the trial, reread your report and notes;
• read and carefully consider any other relevant reports you are given by the lawyers;
• if it is some time since you wrote your report, reread any scholarly articles or studies you have referred to in your report and search for any more recent relevant articles;
• try to understand the context within which you will give evidence. What are the likely factual and legal issues in the trial?; and
• give yourself plenty of time. Don’t rush to court.

In the witness box

• Stay as calm as possible. The judge and jury are interested in what you have to say and want your help in understanding the evidence.
• Be modest, courteous and thoughtful; you are creating an impression. Do not rise to the bait even if you think the cross-examiner is behaving badly or ignorantly.
• Always tell the truth but leave out absolutes and emotive adjectives and adverbs.
• Speak in the plainest English you can to answer the questions properly.
• Listen carefully to the questions and don’t try to anticipate where the questioner is going.
• If you don’t know, say so. Above all, don’t speculate.
• Keep answers as short as is necessary to answer the question properly. If you need to offer an explanation, don’t allow yourself to be cut off. Say, “May I explain?”
• If a question can’t be answered in the way the examiner or cross-examiner has put it, say so and offer to explain.
• If you can’t remember something but a contemporaneous record would help you remember, say so.
• If you have aids, such as diagrams, models or instruments, bring them to the lawyers’ attention before you give evidence. And remember OJ Simpson’s glove: practise any demonstrations before court.

Good luck!

Hugh Dillon is an Adjunct Professor at the UNSW Law School. He retired as a Deputy State Coroner and magistrate at the end of 2016. He conducted a number of medical inquests and is co-author of Waller’s Coronial Law and Practice in New South Wales (4th ed, 2010) and The Australasian Coroner’s Manual (2015). He is now a community representative on the Australasian College of Emergency Medicine and has joined Maurice Byers Chambers in Sydney as a barrister.

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