Expert evidence: practical tips for managing party-appointed experts


James RogersAmy Armitage

Large-scale international infrastructure and construction projects always involve factual questions of what, where and when. However, responsibility invariably turns on more intricate questions of cause and effect and expert evidence is usually required, often across more than one discipline. The expert phase is often therefore the most critical, and sometimes costly, part of the arbitration process. This article offers some practical tips for managing party-appointed experts in arbitrations.

Selection of party-appointed experts

It goes without saying that it is important to select the right expert. This means ensuring not only that the expert has the appropriate qualifications, technical expertise and reputation in the relevant field, but also (if possible) suitable experience of the dispute process and of writing expert reports and giving evidence in adversarial proceedings.

However, credibility is the key consideration. It is vital that any expert has the right technical experience and can convey their expertise in a persuasive and credible manner to a tribunal of lay people, likely unfamiliar with the topic, while remaining impartial and uninfluenced by instructing counsel.

It also helps if the expert is collegiate and good to work with. This is a delicate balancing act. Not everybody possesses the necessary interpersonal skills and is able to engage a tribunal and explain complex technical issues in a convincing and credible manner.

Therefore, it is always preferable to interview potential experts where time permits. Test the expert. Also take soundings from other individuals or practitioners who are familiar with the expert.

It is also worth checking whether the expert remains active in their relevant field of expertise and to check on their published writings – have they previously written anything which conflicts with the position they are adopting in the arbitration? Likewise, make sure that the expert has the capacity to take on the appointment and can meet the relevant procedural deadlines and attend the hearing.

Scope of the expert's role

The expert's remit should be clearly and precisely defined in their written instructions. This requires that the issues in dispute are clearly defined between the parties. Early meetings with the expert as the case develops, and between the experts once the case is afoot, can help to delineate the issues and points of disagreement. It is therefore advisable to instruct experts as early as possible.

The expert must also recognise that their role is ultimately to advise the tribunal independently, rather than to advocate the client's position. This duty overrides any duty to the instructing party.

The primacy of the expert's independence is recognised, for example, in the International Bar Association (IBA) Rules on the Taking of Evidence in International Arbitration, which require expert reports to contain a statement of independence from the parties, their legal advisers and the tribunal. The IBA rules also contain a duty to disclose any existing or past relationships with any of the parties, legal advisers or the arbitral tribunal.

It is not uncommon for experts to be appointed at an early stage during the life of a project and to advise a party on an ongoing basis of the strength of its position. However, difficulties can arise if the expert is subsequently asked to provide independent expert evidence to a tribunal during the course of an arbitration. There is a risk that the expert may be perceived as a 'hired gun' lacking the required impartiality to fulfil the role of an independent expert witness. In all instances, but in this scenario in particular, it is important that the expert's instructions clearly scope out their intended role and that they may subsequently be required to act as expert witness and therefore remain impartial.

An expert will typically summarise the substance of their instructions in the expert report and instructions given through the life of a dispute may become disclosable. Instructions should be drafted with this in mind, in a neutral tone without conveying any comments on the merits or strategy of the instructing party's case on the technical issues.


The more objective and independent the expert appears, the more credible they are likely to appear in the eyes of the tribunal. Experts should avoid acting as advocates for the party appointing them and should be encouraged to concede points where it is appropriate to do so.

It is also important that experts do not stick rigidly to a one fact scenario but be prepared to consider a range of possible outcomes depending on the tribunal's findings on disputed points of fact or law.

Expert evidence should always be rigorously tested by the instructing legal team to ensure that the expert has been objective and has properly considered the contrary views and explanations provided by the opposing expert. One way of testing this is to ask whether the expert would express the same opinion if given the same instructions by the opposing party.

Experts who ignore evidence which is not helpful to their own party's case or consistently choose an interpretation or approach that gives their instructing party the benefit of the doubt will inevitably run the risk that less weight will be attached to their evidence by the tribunal or that the evidence of the other expert will be preferred wholesale.

Credibility is always the key consideration. An expert's lack of credibility may bring into question other aspects of the client's case and the client's and counsel's own credibility.

Giving of evidence

The general aim in every case is to simplify what is often difficult technical evidence into an easily understandable format. This is equally true for written reports, technical presentations (which are increasingly used during hearings) and responses to cross-examination.

Counsel can play an important role in ensuring that written expert reports are presented in a sensible, easy-to-follow format and appropriately summarised. However, the expert must not delegate their opinions to others. The expert must own the report.

Expert witness conferencing or 'hot tubbing' has become increasingly popular in international arbitration hearings. This is a process in which experts provide evidence concurrently (as opposed to sequentially) with the tribunal leading a discussion. Rather than traditional cross-examination, experts are brought together before the tribunal and are encouraged to discuss and debate their differences.

This can be an effective and constructive means of obtaining relevant evidence on technical matters and can save time and costs. At the very least, a genuine analysis of the issues is promoted and experts are often more honest with their views when confronted by a peer. However, it does require the tribunal to be extremely well prepared to ensure that the process stays focused and is properly managed.

Tribunal-appointed experts are more regularly seen also. Sometimes opposing experts can take fundamentally incompatible approaches, not engaging each other's views and opinions. Party-appointed experts are therefore usually asked to confer and attempt to reach an agreement and record in writing the points of agreement or disagreement between them. However, a third expert appointed by the tribunal can help to break deadlock in such situations.

A tribunal-appointed expert will add to the cost of proceedings though, as the parties will still retain their own experts.

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