The Role of the Expert in Advocacy

The idea that experts have a role in advocacy seems an odd topic: after all, experts are required to be independent of the parties and, while it is not required by any of the leading institutional rules,[2] most experts now include some form of declaration in their reports to say that they are giving objective opinion evidence on the matters on which they are instructed. A corollary of being objective is that some experts like to think of themselves as being above advocacy, giving their evidence from the lofty heights of independent thought; at the opposite extreme, there are other experts whose evidence provides just what they think their clients want them to say. In practice, neither of these attitudes is helping the client, the instructing counsel or the tribunal.

Perhaps the most important idea for counsel and experts to remember is that, while an expert is not an advocate for the case, he or she is part of the process of advancing the case, so needs to be thought of as contributing to advocacy.

This chapter is written from the perspective of an accounting and damages expert, but the same principles apply to expert evidence of all disciplines. As with the rest of this Guide, it is addressed primarily to counsel, but it is hoped that experts will also find it useful as a guide to their role. Its aim is to identify the expert’s role at each stage of the arbitral process, and discuss how to get the best out of the expert in a way that contributes effectively to advocating the case.

First is a discussion of the choice of expert, a decision that should be taken early in a case and one that can have a significant impact on the way the case is presented and on the eventual outcome, before considering how to manage experts and ensure coordination between disciplines.

There follows a consideration of expert reports. While every expert will have their own style, there are some general principles that should be borne in mind when working on expert reports, with variations when dealing with reply reports. The concept of a joint document (whether it is described as being a joint report, memorandum or statement) is becoming more common, so the approach to them is discussed, with suggestions on the form of joint statements.

Moving on to the final hearing, experts have multiple roles, culminating in their oral evidence. This provides many opportunities for the expert to affect the case, positively or negatively, and is often the real test of that initial decision regarding the choice of expert. Another chapter deals with the cross-examination of experts, so here this topic is limited to some thoughts from the expert’s perspective.

Selection of experts

Other chapters emphasise the importance of identifying and clarifying the case theory, linking the facts and law to the desired outcome. Part of that case theory will involve areas that require expert evidence, which falls into several types (that are not necessarily mutually exclusive): identifying facts, interpreting facts and giving opinions.

It is normally assumed that experts are there only to give opinion evidence – that was the origin of all expert evidence – based on a matrix of assumed facts. But that presupposes that the facts on which the opinion is to be based are readily accessible and (ideally) already established. The real world is rarely so straightforward, however, so the first role of the expert may be to identify the facts on which his or her opinion is going to be based, through research of the documentary evidence or discussion with the client in collaboration with counsel, and using publicly available information.

Having searched the underlying evidence, an expert can then fulfil the role of interpreter – translating the technical aspects of the underlying factual evidence into a form that can be understood by counsel and the tribunal. This role is often overlooked, or thought of as a side issue to the expert’s opinions, but it can be the critical aspect of expert evidence. Once the fact evidence has been explained by an expert, the conclusions to be drawn may become obvious.

The importance of a competent expert cannot be overstated

The importance of a competent and professional expert cannot be overstated. Experienced experts are expensive, especially in cases requiring complex questions of delay analysis and damage quantification. It is understandable that parties can often be reluctant to make a considerable investment in leading experts; however, it is an investment that is always worth making. I have personal experience of a number of occasions when an otherwise potentially strong case failed because of a flawed expert analysis. Even when a tribunal is otherwise persuaded that a party has a good case, it will not be able to eventually find for that party unless it has detailed and cogent evidence to support the findings when they write up the award. Careful arbitrators tend to be conservative in their decision-making and are looking for a strong and reliable evidentiary basis to reassure them that their decision is the right one.

– Stephen Bond, Covington & Burling LLP

Experts win cases

Asked, long after the fact, by losing counsel in a case where the weaknesses in his advocacy, if any, lay, I offered two simple words: ‘Your expert.’ That was the truth.

Expert evidence is of the essence in any dispute in arbitration that has the least technical dimension. In more cases than one might imagine, outcomes turn on evidence of a more or less specialised nature. Most leading international arbitrators are generalists and, albeit to a somewhat lesser extent, so too are most leading international arbitration counsel. Expert witnesses plainly fill this gap. Even in disputes having no particularly specialised character, if monetary relief is forthcoming, so too will be expert evidence on damages.

Because arbitral tribunals gauge carefully the objectivity and reliability of expert witnesses, counsel need to admonish experts that poor expert performance can sabotage what might otherwise be a winning case. Who are the experts to avoid? Those who display excessive partisanship, undue defensiveness (including taking umbrage at challenges to their credentials), inconsistencies with prior statements (including prior writings and testimony) and an unwillingness to make strategic concessions.

– George A Bermann, Columbia University School of Law

Almost every international arbitration involves a claim for damages, so counsel’s natural inclination is to seek expert evidence on loss or damage. But stop for a moment: does the case really need expert evidence? It might be that the loss is clear enough to be argued without expert support. Assuming that this is not one of those cases, however, the loss is likely to result from an analysis of what would have occurred had the cause of action not arisen; counsel needs to consider (at an early stage) who is going to be responsible for devising the hypothetical scenario that is going to form the basis for the expert’s quantification. Can it be left to the expert, or is it likely to require input and discussion from others?

Having thought about what sort of expert evidence is going to be required, counsel can then consider the choice of expert. The basic qualities required of the expert are obvious – independence and authority – but that is not all.

There is a difference between a good expert and a good expert witness. In most walks of life, professionals of any discipline spend most of their time working alongside or speaking to other professionals with similar knowledge (lawyers speak to lawyers, doctors work with medical practitioners, accountants work with financial people, civil engineers work with architects and builders), so they routinely use jargon and shorthand, because they know they will be clearly understood – indeed, the use of jargon marks them out as specialists, enhances their credibility among their peers, and shows that they are privy to the secrets of their profession. An expert witness is in a very different position: their role is going to be to demystify their technical expertise, something that many experts find difficult or even counter-intuitive. A key quality needed of a prospective expert witness, and one that will enable him or her to contribute to effective advocacy, is a genuine willingness and ability to explain – in fact, it can be more important than expertise per se.

Finally on this topic, do not forget about the team supporting the expert and especially the expert’s second-in-command. Counsel needs to have almost as much confidence in that individual as in the expert themselves, especially when the proceedings draw towards a hearing (see below).

Instructing experts

Having decided that you need an expert, and found someone who seems to fit the bill, it is important to give your expert the right instructions. This is not as easy as it sounds: counsel understand the case, and the case theory, so can see what is needed by way of expert evidence to plug the gaps. But experts speak a different language and have different knowledge, so counsel should be prepared to discuss and explain their case theory to the expert, to allow the expert to see where his or her intended contribution is going to fit in the jigsaw puzzle of evidence, and perhaps make suggestions as to what he or she can provide and the questions he or she can answer. A sign of a good specialist is the ability to tell you the question you need to ask to get the answer you are seeking, so allow your expert to do that.

There is sometimes some mystery about ‘instructions’ and what they comprise but, fundamentally, there are only two types of instruction: the topics for the expert to consider (which might be set out as a series of questions for the expert to answer) and the assumptions that the expert is being told to make. Everything else that passes between counsel and expert, such as discussions as to the merits of different approaches, the availability or otherwise of data, and possible lines of enquiry, is not part of the expert’s instructions and, therefore, will not need to be referred to by either counsel or expert.

Assumptions come in several flavours:

  • Some are clearly not matters for the expert:
  • general assumptions (for example, that the respondent is liable or that the claim succeeds);
  • factual assumptions (for example, that certain data or information is reliable); and
  • legal assumptions (for example, the meaning of a contractual requirement).
  • Some are in a hybrid area, in which both expert and counsel might be expected to have a view (for example, the date at which to assess damages or values, or the appropriate basis for evaluating loss). Counsel and expert will need to be coordinated in their view, so that the position is argued by one or the other, but not by both, and to ensure that they are consistent. This failed in a recent case, when opposing counsel pleaded that the shares should be valued at ‘fair value’ but the expert adopted ‘market value’ as the basis of their work.
  • Some are matters that fall within the expert’s field of expertise but either the expert’s opinion is not being sought or the expert is not being allowed to reach his or her own assumption (for example, an expert being instructed to rely on an interpretation that he or she knows is unrealistic). These are commonly dealt with by counsel instructing the expert and the expert making that explicit. In those circumstances, the phrase ‘I am instructed to assume that . . .’ suggests that counsel has imposed the assumption on a reluctant expert whose view is not in line with counsel’s or the client’s view – no one will be fooled and the truth is likely to come out on cross-examination.

Occasionally, counsel (and more often their clients) want their experts to support every aspect of the case. However, it is not a good idea to restrict the expert to using assumptions only in the client’s favour: this is especially important when dealing with areas such as damages, which can depend on a series of assumptions that might not all go in the same direction, and where the expert should be allowed (or instructed) to deal with a range of permutations. An expert who only deals with one-sided assumptions looks biased, even if just following instructions, and becomes a poor advocate for his or her own position and for the case as a whole.

It might be thought that the instructions to an expert need to be clear and consistent from the beginning. In a perfect world, where the case is clear from the start and the other side will not raise anything unexpected, that would indeed be the case, but counsel and expert both need to show some flexibility to take account of new evidence and arguments as they arise. This can be dealt with easily by adding new instructions as and when required, with the final formal ‘letter of instruction’ (if required) being a summary of all the instructions that have previously been given.

Case management and coordination

Counsel running a case have many strands to coordinate: documents, fact witnesses, expert witnesses, precedent, legal argument – and a demanding client. It may, therefore, be tempting for the counsel team to feel that everyone (including experts) will be more efficient if they stick to their own area of expertise and do not get diverted by interesting points that are in others’ territory. There are cases in which that will work, but they are the minority – more often, experts can contribute better to advocacy if they understand what is going on around their evidence, and how they fit in with the rest of the case. They will then be alert to issues that arise in their work that are peripheral to their own area but that might impinge on other parts of the case.

An example of this aspect of case management is document production. Experts can be helpful in identifying what documents to request, how to go about specifying them with reasonable particularity, and in assessing the resulting production. They can also help to spot the gaps: the documents that would be expected of a properly run business but have not been produced, or the existence of which is denied. While this might seem reasonable from a legal viewpoint, an expert may have a very different view and may be able to draw inferences that counsel can use elsewhere.

Keeping experts in their own silos becomes a bigger issue when dealing with multiple experts, especially when their personal areas of expertise overlap (for example, in a particular case, there were different experts on each of the regional gas market, gas price economics, gas price reopening clauses, technical aspects of gas transmission and quantum). In that situation, it helps if the experts themselves are part of the discussion as to which expert deals with which issues, the aim being to avoid overlaps (protecting against more than one expert being challenged as to the reasons for nuances of difference between them) and gaps (when it is not clear who is responsible for a particular topic of evidence). Multiple experts can also assist counsel and each other by testing one another’s conclusions, based on their own linked expertise – experts with different experience can bring an extra element of commercial reality to one another’s views, and thereby help each other become more persuasive.

Experts vary in their attitude to challenge, but a good expert should be comfortable with being challenged on his or her views, and should be able to explain to counsel the strengths and weaknesses of his or her own position. This type of challenge should take place as early as possible in the case, preferably before the expert has reached a final opinion – in a difficult case, it might be beneficial for counsel to seek a preliminary opinion from the expert on a contentious point, well before formalising instructions and perhaps before formalising the expert’s appointment.

Much management of and coordination with the expert will be achieved through draft reports or advice notes, which should give counsel an opportunity to see where the expert’s views are heading and give both counsel and expert a chance to test whether they are heading in the right direction. One part of that exchange will be to settle on the outline of the expert’s written report.

The report – the expert’s main contribution to written advocacy

There are as many ways to write an expert report as there are experts, and this chapter does not pretend to offer unique insight in to how best to write a report, but an expert’s reports are going to be the majority of their evidence and, hence, the basis of their contribution to advocacy, so need to be prepared with that in mind. Here are some points for counsel and expert to consider together.

Know the audience

An expert report is required because there are gaps in the evidence that need to be filled through the application of expertise. So it is not a vehicle for the expert to demonstrate his or her erudition, nor is it intended to be a written lesson in an aspect of the technical specialism. The writer of an expert report needs to bear in mind not only its objectives but also its audience.

The primary audience is the tribunal. There will be secondary audiences (the opposing counsel team, the opposing expert) and other important parties (such as instructing counsel and the client) but the primary purpose of the expert report is to persuade the tribunal that the expert’s opinions and views are fair and reasonable, and more reliable than those of the opposing expert. It is therefore a good idea for counsel to give the expert some insight about the tribunal: who they are, their specialist areas, their experience, etc. The expert can then tailor the report so as not to expect knowledge that the tribunal does not have, or can recognise that the tribunal already has some knowledge and will be able to follow an argument differently.

In most cases, the tribunal will be wholly or partly made up of lawyers; for a quantum expert, for example, that means a group of intelligent laypeople who may have little understanding of accounting concepts or terminology and are not entirely comfortable with numbers. The report needs to be drafted with that in mind, so that it takes the reader through the arguments from first principles and explains them in a way that is intelligible to non-specialists, which is better (and more subtle) advocacy than simple assertions would be. This will sometimes result in a need to define terms that the expert might think are already well understood, such as earnings before interest, tax, depreciation and amortisation (EBITDA) and discount rate, and to explain what they mean and why they are useful.


There is a simple rule for an expert report (which, like all rules, can be broken): never use a technical term without first explaining it. That is easily said, but is more difficult to implement because the term must be explained, not just defined.

Explaining technical terms is part of the expert’s role of demystifying his or her expertise, and provides an excellent opportunity to gain the confidence of the tribunal by answering the unspoken questions that an intelligent person would ask. For example, consider the term EBITDA, which might be described as a proxy for operating cash flow. This begs a series of questions, such as:

  • What are earnings? If earnings are important, why are we interested in earnings before deducting other things?
  • What is depreciation? What is amortisation? What is the difference between the two?
  • Aren’t interest and tax real cash costs?

By anticipating and answering these questions, the expert demonstrates his or her expertise and shows that he or she is not trying to hide behind what the tribunal might see as obscure terminology.

Most importantly, this rule applies to those technical terms that are not obviously technical terms, because they also have an everyday meaning that may or may not accord with the technical meaning, and those terms that might have multiple meanings. Here are some frequently encountered examples:

The possibility that something will go wrong‘There is a risk of rain tomorrow’
A measure of the relative volatility of the price of a share compared to the market‘Risk is measured by the beta’
Something to be avoided‘That’s a high-risk strategy’
A reduction in price‘Buy now – 50% discount’
To anticipate and make allowance for something‘The stock market discounts all known facts about the company’
To ignore something‘I discounted the possibility of missing the train’
A means of recognising the time value of money‘The expected future cash flows are discounted at the cost of capital’
The relationship between market price and net asset value‘The investment trust’s shares are quoted at a discount of 15%’

Identifying these sorts of situations, when words are being used in a way that is conventional to the expert but would not automatically be understood by the tribunal, is difficult, and relies on good communication between counsel and expert.

Summary – at the beginning or at the end?

Counsel usually write pleadings and submissions in what is known as a ‘pyramid’ style, starting with the top of the pyramid (‘our case is right’) then justifying it through a succession of legal and evidential points. This style of presentation works best when the conclusion is the most important thing, and is perfectly suited to making an argument then bolstering it.

An expert report is different. The expert is expected to approach his or her work with an open mind, and give honest and objective opinions based on the evidence available and assumptions given by counsel. If the expert gives the answer at the beginning, the report might create an impression that the rest of the report is seeking for the best evidence to support a conclusion that has already been reached.

One view is that it is better for an expert report to begin with the questions that need to be answered, then consider the evidence available and gradually use that evidence, together with reasoning and expertise, to arrive at a series of conclusions. This ‘build-up’ approach can be applied to individual sections within a report, as well as to the report itself. It has the advantage that it takes the reader through a journey, examining the evidence in the light of the questions to be answered and the expert’s knowledge, and helping the reader to draw conclusions with which he or she agrees. If this is done well, the reader reaches the conclusion for himself or herself at the same time as the conclusion is spelled out in the report, which would be excellent advocacy.

An alternative view is that a non-technical reader is likely to find an expert report difficult to follow without an early indication of where it is going. Summarising the conclusions at the beginning provides that road map, so that the reader can see the significance of matters as they are raised, but it then becomes important that the summary is drafted in a way that demonstrates the open mind that the expert has adopted. The advantage of this approach is that the impact of the report does not depend on the members of the tribunal having read and understood it in full at an early stage.

Deciding on where to put the summary might, therefore, be thought of as a balancing act, between counsel’s confidence in the expert’s power of explanation and counsel’s confidence in the tribunal’s power of concentration and available time.

Graphs and diagrams

Bearing in mind the target audience for an expert’s report, it is tempting to focus on words as the medium through which to explain everything, even when the expert’s natural tendency when communicating with fellow professionals would be to use diagrams and graphs. However, there can be considerable benefit in providing visual aids in an expert’s report, providing the report takes the time to explain the purpose of the diagram and the conclusions to be drawn from it, neither of which will be obvious to the untrained reader.

There is a danger of over-complexity in diagrams. Taking the example of a diagram of a series of transactions, it is tempting to add more and more detail until it ends up as a spider diagram with annotated arrows pointing everywhere, which will be incomprehensible to someone unless they have read through all the transaction documents, at which point, the diagram will have achieved nothing. It would be more effective to introduce the trans­actions individually and build up aspects of the diagram gradually, so as to give the reader time to absorb each step before the next one is explained. The final result will then be a complex diagram that the reader has already understood, leaving it open to the expert to highlight the critical features at the end.

Graphs are also a target for complexity. Most of us can absorb only a limited amount of information from a graph and need to be told what to look out for, otherwise we might focus on the wrong aspect and, hence, draw the wrong conclusion. It is better to use graphs to make straightforward points in an interesting way, keeping them simple, and avoiding unusual types of graphs. That might seem unimaginative in comparison with, for example, newspapers, but is more sensible for most experts, who do not have access to data visualisation specialists.

Responsive expert reports

In the same way that a respondent might have either a positive or a negative case, a responding expert might be putting forward positive opinions or only responding to the opinions given by the first expert. Whichever is the case, the responding expert starts on the back foot (the other expert has already demonstrated his or her expertise) so may need to work harder to establish his or her expertise and counter the views that have been expressed.

This is when experts’ reports can easily verge on the partisan and become less objective. It is unlikely (although not inconceivable) that, even if the responding expert disagrees on some important points, the other expert is completely wrong. Trying to give that impression can therefore be a bad idea: rather than appearing to be superior, it might suggest a refusal to accept anything detrimental to the case, no matter how reasonable, that detracts from the responding expert’s credibility and objectivity.

Responding experts need to consider what matters. It is sometimes easy to compile a long list of points of disagreement, most of which are of little, if any, consequence to the opinions expressed. The responding expert then has options: for example, he or she could highlight a list of unimportant points of disagreement to imply that the other expert has been careless, or the case might be better advanced by focusing on critical points and using the list as a supporting argument that their views are to be preferred. However, it is advisable, especially when criticising another expert, to double-check and triple-check every last point, no matter how minor: every expert enjoys responding to criticism in kind.

An important role for a responding expert is to identify and focus on the assumptions made by the first expert, especially those implicit assumptions that have not been highlighted. Finding implicit assumptions allows the responding expert to suggest that the first expert has not been entirely open in their report, as well as giving a basis for exploring alternative scenarios and, hence, reach different conclusions.

A responding expert has the chance to test the conclusions presented by the first expert from the point of view of an expert rather than only from a legal angle. This can be done by taking the first expert’s opinions and extending them to their logical consequences, whether positive or negative. A common example is the ‘hockey stick’ financial projection, whereby the expert presents a situation in which a recent decline in the performance of the subject business is about to reverse dramatically, leading to rapidly growing profits in contrast to historical losses: this can be tested against the actual outcome of others in a similar market that have been unaffected by the cause of action, showing the unlikelihood of that success.

Assuming the proceedings follow the memorial style, with two rounds of submission by each party, the experts will also find themselves replying to each other in turn. In a perfect world, this would result in a series of ever-shorter reports, as the experts iron out differences between them; more commonly, the experts will both become more entrenched in their views and reluctant to accept that the other experts’ views have any merit. Assuming there is no requirement for a joint statement, the last report to be prepared has the advantage of being the last written word from the experts. It is therefore an opportunity for that expert to summarise both experts’ positions, highlight the reasons for differences between them, and be seen by the tribunal as the more helpful expert and, hence, the more effective advocate of the expert evidence.

Joint statements

A useful tool for tribunals, and therefore something to be considered by counsel for possible suggestion to the tribunal, is a joint statement (or report or memorandum) by experts of the same discipline. The purpose of a joint statement is not (as might be thought) to give each expert a chance to advocate a position and persuade the other; rather, it is a vehicle for summarising the areas of agreement and clarifying the disagreements between experts, and explaining the reasons for those disagreements. It then gives the tribunal a checklist of matters that affect the expert evidence, whether they be reliance on different versions of the facts, being instructed to use different assumptions or genuine differences of opinion.

There are two basic forms of joint statement: columnar and textual. Both have their merits and, in some cases, it is helpful to use a mixture of the two approaches.

  • Columnar statements have their origin in the Scott Schedule, which is widely used in construction cases. They provide a list of topics, then give the view of each expert on each particular point.
  • Textual statements are more discursive, dealing with broader topics, then, for each topic, summarising the points on which the experts agree and those on which they disagree, and finally giving a summary of each expert’s position on the points disagreed.

In both types of joint statements, it is better to refer back to detailed explanations in the experts’ reports rather than repeat them, otherwise the joint statement will become too cumbersome and will be impossible to agree.

One of the obstacles to the wider use of joint statements is counsel’s understandable reluctance to lose control of an expert and risk seeing their expert’s views expressed poorly. Recent experience shows that tribunals have made very favourable comments on joint statements that are clearly the product of the experts (as shown by the lack of legalistic wording) and provide clear explanations of the reasons for differences.

Before the hearing

In the lead-up to the hearing, counsel will be focused on planning their oral advocacy. Perhaps the expert’s most important contribution is in identifying issues that are suitable for cross-examination of the opposing expert, and then ensuring that counsel understands them well enough to be able to cross-examine with the knowledge that they can deal with any unexpected answers. This requires the expert to be capable of putting themselves in the other expert’s shoes, and thinking about the case from a different perspective, so as to anticipate how the opposing expert is likely to deal with a set of questions.

Experts can also assist counsel in preparing the cross-examination of those fact witnesses whose evidence is the foundation of the assumptions that have been made in the expert evidence. These will have become clear earlier, during preparation of the experts’ reports, when the source for every assumption will have been considered. The expert can help by identifying the weaknesses in the fact evidence, as well as the areas where oral evidence can strengthen a party’s own position.

Trust your experts and tribunal!

Recently, I chaired a London-based arbitration where, after first receiving consent from counsel, the tribunal was able to conduct a separate meeting with the quantum experts. The discussion took place prior to the hearing on the merits, but already after the filing of two rounds of expert reports. The findings of the experts on rather complex issues differed considerably and many assumptions and deductions, in particular with regard to the lost profit calculations, could not be reconciled.

Leading up to the meeting with the experts, the tribunal confirmed with counsel the scope of issues to be discussed and distributed a detailed agenda of topics. The tribunal also made clear that any remarks made by its members during the meeting would be without prejudice to its findings on the merits and made solely for the purpose of facilitating the tribunal’s understanding of the expert testimony.

The experts were cooperative and forthcoming during the day’s discussion. There was an open discourse among the experts and members of the tribunal. The experts were given the opportunity to provide their input and feedback on the various subjects set out by the tribunal. The overall atmosphere was more collegial than one normally encounters in a cross-examination setting.

The assembly proved to be very helpful for all parties involved. In the end, the tribunal was able to better understand the points on which the experts were in agreement, as well as the points where there was a clear difference of opinion. An added benefit of the meeting was the identification of documents that both experts were interested in seeing to further update their findings. Although quite onerous to prepare for, the process allowed the tribunal to head into the hearing on the merits with a clearer understanding of the experts’ opinions and consequently, the parties’ respective cases. Ultimately, as a result of such an exercise, the presentation of the experts and their cross-examination at the hearing will be more focused and useful.

– Georg von Segesser, von Segesser Law Offices

One aspect of the planned expert evidence is the relationship between the opposing experts, which counsel needs to consider carefully. There will be opportunities for the tribunal to compare the experts and their evidence, perhaps through ‘hot-tubbing’ in some form or through oral presentations, and counsel needs their expert to give honest advice on the respective strengths and weaknesses of the expert evidence so as to take a reasoned view as to the procedure to request.

There is also a role for the expert in helping counsel prepare their opening submissions. While it is the expert’s role to deal with his or her own evidence, counsel needs to be able to take the tribunal through the key aspects of that evidence, so is likely to need some education from the expert on the basis for his or her conclusions and why they are to be preferred to those of the other expert.

At the hearing – the expert’s contribution to oral advocacy

By the time of the hearing, the expert is probably looking forward to the opportunity to persuade the tribunal that his or her opinion is to be preferred, so counsel might need to remind the expert that his or her role is limited to his or her area of expertise, and that he or she is not the principal advocate of the client’s case.

When counsel is speaking, there is little that the expert can contribute, apart from being sensitive to the reactions of the opposing side and its expert. A good policy is for counsel to explain to the expert what is needed: most counsel do not want lots of notes being passed, but would like a note when something important arises, if only as a reminder to discuss the point at the next break. The expert is there to contribute when needed, recognising that his or her role relates to only one aspect of what may be a highly complex case with many moving parts, all of which counsel is trying to manage.

Counsel should consider whether an expert needs to be present when relevant fact witnesses are giving their testimony. There may be a benefit in the expert being alert to points that can be challenged through the use of expertise, and potentially used in due course in the expert’s oral evidence; the disadvantage is that it becomes harder for the expert to avoid having to deal with unexpected points raised by fact witnesses that affect his or her assumptions or conclusions. Providing transcripts for review might be a middle ground.

Once the hearing gets to expert evidence, the tone may change. The tribunal should see the expert witnesses as being on the tribunal’s side, and be willing to pose questions and seek clarification during the expert’s oral testimony.

There is a growing trend of expert evidence beginning with an oral presentation, often accompanied by slides, subject to an agreed time limit (perhaps 15 to 20 minutes). From the expert’s point of view, this is an opportunity to focus on the points that he or she wants to make, and to make them clearly and succinctly, in contrast to the rest of his or her oral evidence, which will be cross-examination under the control of the opposing party’s counsel. The expert needs to be selective and focus on what really matters, because this will be the only chance to spell out his or her position without any interruption, and it is a great opportunity to persuade the tribunal of his or her expertise and willingness to be helpful.

The oral presentation may have been prepared in advance, but the expert should be ready to discuss it with counsel shortly before delivering it, with a view to adding or subtracting points that have become more or less relevant during the hearing so far. As with written reports, the message for the expert is to focus on the audience in the presentation: speak to them, not at them; don’t read out the slides; and provide the backup and references on the slides so that the tribunal can find the sources for everything said.

In contrast, cross-examination can seem very defensive, with the expert trying hard not to concede points to opposing counsel. But counsel should make sure their expert understands that it is not part of his or her role to either concede or not concede: he or she is there to give an expert opinion in response to questions, whether or not those opinions are in favour of the client. Experts will frequently be posed hypothetical questions, designed to draw out adverse opinions, and should always give honest and accurate answers, albeit on the basis of the (not accepted) hypothesis posed.

During an expert’s cross-examination, his or her assistant becomes a key attendee. Counsel is constantly needing to consider whether any points made by the opposition require a response through re-examination. The assistant can help to explain why the expert has answered in a particular way and, if counsel decides to seek clarification, can help counsel to phrase re-examination questions in a way that is not leading but will be understood by the expert.

Some form of concurrent evidence, or ‘hot-tubbing’, appears in many cases, with experts sitting together to respond to a tribunal’s questions. For counsel, this is a risky moment; for the expert, it may be uncharted territory. Much has been written about hot-tubbing and the tactics to be adopted by counsel; in practice, counsel needs to trust the expert to respond to the tribunal’s questions and the opposing expert’s views in an authoritative and professional way, again using the expert’s assistant to spot issues that need clarification.

In conclusion

There is a tension built into the role of an expert witness, with the need to be objective and independent, and a duty to the tribunal, potentially conflicting with the expert’s natural desire to help his or her client’s case and his or her professional obligation to the client. Accountants, who are familiar with the role of auditors, who have responsibilities to shareholders as well as management, may find that dual role easier than many others who have never encountered it before. That tension means that experts may need to be reminded that their role is to be experts, not advocates.

An expert’s role is, first and foremost, to reach professional opinions on matters for which he or she is qualified and then to explain those opinions. This chapter has discussed how counsel will have taken responsibility to the client for selecting an expert whose opinions assist the case, and how the expert will have contributed to advancing the case through his or her written and oral evidence. The expert’s contribution to advocacy is perhaps best summarised in a single phrase: the expert’s role is to advocate his or her opinions, not the client’s case.


[1] Philip Haberman is the senior partner of Haberman Ilett.

[2] The IBA Rules on the Taking of Evidence in International Arbitration 2010 require experts to be independent of the parties, but say nothing about the content of their evidence. The Chartered Institute of Arbitrators protocol on the use of party-appointed experts says that they should be impartial and have an obligation to assist the tribunal. The ICC, LCIA, UNCITRAL and ICSID rules (among others) permit expert evidence but impose no requirements on experts.

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