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Expert evidence is an important part of litigation and cases can be won or lost on the performance of an expert in court.
Selecting a suitable expert for a particular case is not easy, but the consideration of a number of practical matters at the outset can help to avoid a disappointing performance.
Counsel for the opposition will try to undermine the credibility of an expert witness by suggesting that his expertise is limited in some way. It is important to identify the exact issue in dispute and examine with the expert, the clients and others in the relevant discipline whether he is genuinely a specialist in this area.
Many disciplines embrace a variety of different specialisations - for example, a surveyor giving evidence on property values may be a specialist in rental values rather than sales.
This is also something which needs to be kept under review as the various issues emerge during the course of the proceedings.
There are many fields in which an expert will enlist the help of others, either to do the leg work, or to give assistance on a specific aspect. For example, an engineer may ask others to carry out detailed calculations or investigations. It is important to be aware that this is happening and to consider whether the person being used as an expert witness should give direct evidence themselves.
The right qualities
The qualities which make a good expert witness are not necessarily the same as those which make him an expert in his field - eminence is no guarantee of a good performance.
The process of writing an expert's report, analysing the evidence held by the opposing party in a case and dealing with cross-examination may be very different from the activities which, for example, a derivatives trading expert normally undertakes.
Ability to analyse
Fine distinctions can be important in litigation, and an expert will be asked to approach the issues in an analytical way. A broad-brush approach is likely to be unsatisfactory. For example, the expert may need to deal with a variety of hypotheses on issues relating to causation, which would not often arise in normal practice.
Large numbers of documents can be produced in litigation, particularly during discovery. These documents may appear in a piecemeal fashion and may not ordered or easily accessible. The expert needs to be able to get to grips with the paperwork and be prepared to assess the impact of the documents obtained and consider what further requests should be made for documents and/or enquiries from the opposing party.
An expert's report will be examined in detail by the other party's specialist witnesses and lawyers to pick up any mistakes, inaccuracies, inconsistencies and lack of precision, however trivial. Even if individually insignificant, when added together any mistakes can create a bad impression.
When giving evidence the expert may also need to go into the theory behind his conclusions to explain and justify matters which seem self-evident to him and his profession.
Dealing with questioning
The expert will need to be able to deal with questions from the judge on cross-examination.
He should be able to listen to a question and then answer that question alone, fully but concisely. He should be able to hold his position under pressure but not be dogmatic. He should also be able to resist becoming impatient or, worse, losing his temper.
It is important to go through with the potential expert exactly what work will be involved to ensure he is available when needed. The preparation of the expert's report can be time consuming and his assistance will probably be required in connection with matters such as requests for further and better particulars, discovery, witness statements and so on.
The expert should be given an estimated timetable but also warned that the nature of the court system means it is liable to change.