The art of giving expert evidence

The court is a daunting place for the uninitiated. Gerry Lagerberg provides survival tips for the first-time expert witness. Gerry Lagerberg is a partner in PricewaterhouseCoopers dispute analysis and investigations practice.

Lawyers and expert witnesses often have common objectives in a case but there are some major differences in their courtroom priorities. These should be properly understood on both sides at the outset of a case.

The expert’s opinion may not be everything that the lawyer wants to hear, but that is no bad thing. The good expert’s skill and objectivity, properly used, are effective dispute resolution tools and their evidence is a key element in a lawyer’s strategy.

Both the lawyer and the expert have duties to the court. But the lawyer’s additional duty to do the best for their client means that it is fair to challenge the expert to see just how far they will go on an issue and the expert should avoid becoming an advocate for one side.

This can be frustrating for the lawyer but the consequences of pulling the expert into a partisan position can be disastrous. Judges can spot a “hired gun” and objectivity is what the court requires. If the technical evidence does not support the desired outcome, the lawyer needs someone who will deliver the bad news as early as possible.

Some experts think that experience and knowing a subject inside out is all that is needed to be an expert witness – the court is just a showcase for their talents. But this is a dangerous misconception.

Lawyers need experts with additional qualities, which include:

A sense of urgency and personal commitment to the case.

The ability to communicate complex issues clearly to a non-technical audience.

The ability to be objective and authoritative.

Expert evidence

Few cases that an expert will be involved in will get to trial but the expert should assume that each case will go that way. In court, the expert faces the scrutiny of the judge and opposing counsel. When giving evidence there are a number of useful pointers that the expert witness should remember (see box).

The expert’s report

A good report should be drafted with two readers in mind. First the judge, who decides the issues, needs to understand the expert’s opinions and how they have reached that opinion.

Second, the other side’s lawyers. Experts need to evaluate the strength of their case and which matters can be agreed by the experts before trial.

The expert’s report should be clear and should usually anticipate and deal with the weak points in the client’s case. If it does not do so, that omission may damage the expert’s credibility.

Tips on giving evidence


Get a ‘feel’ for the trial. Examine the layout of the courtroom and if permitted attend the other witnesses’ cross-examinations.

Make certain you understand the question before answering it.

Be consistent.

Answer questions as directly, concisely, honestly and courteously as you can. Speak clearly so that everyone in the court can hear every word.

Stay interested in what is being said – looking bored will not reflect well on you.

Take relevant key papers with you – leave any other papers at the back of the court.

Be punctual.

Be well prepared.

Address the judge, not the advocate.

Do not:

Let the lawyer establish an unreasonable hypothesis. If it is untenable, you will suffer in the witness box.

Be aggressive or biased.

Give unclear testimony.

Testify outside the area of expertise.

Use technical jargon.

Give a swift answer if you need to pause and consult papers first.

Give the appearance of quibbling or being evasive.

Attempt humour – it is almost always out of place.

Answer ambiguous or equivocal questions without obtaining clarification.

Engage in personal exchanges with opposing counsel – you will lose.

Smile or grimace as counsel score points against each other or another witness.