Introduction

The use of expert evidence (be it from judicial, industry, quantum or delay experts) is permitted in the common and civil law systems that operate in most developed economies.  It is well-established and mature in both international arbitration and litigation proceedings.

However, the experience of the expert can differ markedly, depending upon both the type of dispute resolution mechanism used, and whether the applicable legal framework is common or civil law.  For example, in French litigation, the prevailing tendency historically was for expert witnesses to be court-appointed rather than party-appointed, and experts were rarely cross-examined orally on their evidence - although there have been some changes in recent years.

In this article, we explore some of the nuances and key differences in the approach required in international litigation and arbitration proceedings.

The Duty Of The Expert Witness

The litigation process is typically governed by strict procedural rules specific to the jurisdiction and they may provide guidance on the duty and role of the expert.  As an example, the use of experts in English litigation is addressed in the Civil Procedure Rules, Part 35 (“CPR35”).  This sets out detailed rules covering, inter alia, the appointment of experts, the duty of the expert and the format and content of the expert’s report.  CPR35 also stipulates that the expert must include in his or her expert report a declaration setting out their independence.

CPR35 provides that: “It is the duty of experts to help the court on matters within their expertise” and “This duty overrides any obligation to the person from whom experts have received instructions or by whom they are paid.[i]

In relation to arbitration, however, there are no regulatory frameworks applicable to experts in most institutional procedural rules.  For example, the rules of the International Chamber of Commerce,[ii] the London Court of International Arbitration,[iii] the United Nations Commission on International Trade Law[iv] and the International Centre for Settlement of Investment Disputes[v] allow expert evidence but impose few requirements on party-appointed experts.  In addition, Tribunal members have the authority to adopt procedural measures (including in relation to expert evidence) which, in their view, are most conducive to effective case management.

Many parties use the International Bar Association (IBA) Rules on the Taking of Expert Evidence in International Arbitration, but this is voluntary.  The IBA Rules require that a party-appointed expert is independent of the parties, and that a statement to this effect is included in the expert report.[vi]

Similarly, the Chartered Institute of Arbitrators’ (“CIArb”) ‘Protocol for the use of Party-Appointed Experts’ states that an expert’s opinion shall be impartial and objective, and that an “expert’s duty, in giving evidence in the Arbitration, is to assist the Arbitral Tribunal to decide the issue or issues in respect of which expert evidence is adduced.”[vii]

Adoption of the CIArb Protocol is voluntary, and – as with the IBA Rules - the Protocol explicitly states that it is not intended to limit the flexibility inherent in international arbitration, adding that parties and Arbitral Tribunals are free to adapt it to the particular circumstances of each case.

One new development in this area is the Rules on Efficient Conduct of Proceedings in International Arbitration (the “Prague Rules”), launched in December 2018.  The Prague Rules are explicitly intended to encourage Tribunals to take a more active role in managing the proceedings (as is traditionally done in many civil law countries).[viii] The IBA rules are considered by many in civil law jurisdictions to reflect too closely the common law approach to disputes – in particular with regard to the extensive rights of parties to call witnesses of facts and experts and the assumption that proceedings will feature written witness statements, cross-examination and document production.[ix]

The Prague Rules are not intended to replace the rules of individual arbitral institutions, but rather to supplement the procedures ordered by the Tribunal in a particular case.  Whilst they allow for party-appointed experts, the emphasis is on Tribunal-appointed experts.[x]

However, as of late 2023, adoption of the Prague Rules internationally appears to be very limited, with the majority of international arbitration procedures and judgments still being conducted under the IBA Rules.[xi]

Notwithstanding the apparent lack of procedural rules, it is widely accepted in international arbitration that the expert’s duty is to the Tribunal and that the expert should be independent of his or her instructing party (or both parties, in the case of a Tribunal-appointed expert).

Party-Appointed Vs Tribunal/Court-Appointed Experts

Litigation and arbitration both allow for Court/Tribunal-appointed experts; however, in both forms of dispute resolution party-appointed experts are far more common.

Although Court/Tribunal-appointed experts (or Single Joint Experts, “SJEs”) may appear to be a means of saving costs for the parties involved, it can in fact have the unintended consequence of increasing costs.  One or both parties may hire their own expert to review the SJE’s expert report, to assist in responding to the SJE, and potentially to make submissions to the SJE.

In our experience, parties are often reluctant to agree to a Court/Tribunal-appointed expert due to a lack of confidence in the process.  A key concern is that the Court/Tribunal-appointed expert may become the arbiter of fact or technical issues, thus taking on the role of the Court or Tribunal in relation to some parts of the case.  In addition, parties may be concerned that a Court/Tribunal-appointed expert may not give sufficient weight to their arguments.  Implicit in this concern is an assumption that a party will have greater access to its own appointed expert and therefore, the opportunity to ensure that its arguments are heard and considered.

One difference between litigation and arbitration that is relevant in this regard is the increased scope of the latter to accommodate Tribunal members specialising in a discipline relevant to the dispute.  This may obviate the need for expert evidence in some cases.

Procedural Differences

As noted above, the litigation process is typically governed by strict procedural rules, whereas the arbitration process is not.  The most significant differences between the role of the expert in litigation and arbitration respectively are therefore procedural in nature.

Instructions To Experts

Whilst the IBA Rules, the CIArb Protocol and the Prague Rules encourage early and proactive engagement of the Tribunal with the substantive issues in a case, the authors have observed that, in practice, this is more typically seen in litigation proceedings.

The use of early case management conferences in litigation often results in a more directed scope of expert evidence.  This avoids the risk of ‘ships passing in the night’ – where experts take different and incompatible approaches to answering the same question or even answer different questions.  In addition, the English courts, for example, increasingly direct experts to work together at an early stage to narrow down the issues.  In practice, this might mean, for example, agreeing on relevant valuation dates.  This is the approach envisaged under the arbitral rules referred to above, but in the authors’ experience, this is still not commonly seen in arbitration.

Joint Statements

Joint statements are a common procedural feature of litigation in common-law jurisdictions such as England & Wales, Hong Kong, Canada and Australia.  The purpose of a joint statement is to help narrow the issues in dispute by identifying the matters agreed upon by the experts and explaining the reasons for any items not agreed upon between the experts.

This is not typically required in arbitration, but it is not uncommon to see Tribunals incorporate a joint statement in their procedural directions.  The IBA Rules, for example, state that the Tribunal may order party-appointed experts to meet and attempt to reach agreement on the issues within the scope of their expert reports, and to record in writing any such issues on which they reach agreement, any remaining areas of disagreement and the reasons for such disagreement.

Opening Statements

It is becoming increasingly common for Tribunals to ask experts to make opening statements.  The purpose of these opening statements is to summarise the expert’s evidence and to highlight the key points relevant to the Tribunal’s determination; it is not an opportunity to introduce new evidence, nor is it an opportunity to advocate on behalf of the expert’s client.  In the authors’ experience, opening statements are a valuable opportunity for the expert to set out in full the underlying logic and assumptions behind their opinion, as often cross-examination is limited by counsel to closed-ended “yes or no” questions.

Inquisitorial (Arbitrator-Led) Vs Adversarial (Counsel-Led) Cross-Examination

In contrast to the adversarial cross-examination system prevalent in common-law countries, in civil-law countries such as France, Germany, Spain and others that follow those legal systems, an inquisitorial (i.e. judge or arbitrator-led) system prevails.  A point of view commonly expressed by legal practitioners from these countries is that sophisticated claimants often use expert evidence in adversarial systems to inflate claims.  An example of this strain of thought can be seen in the following quote from Lord Woolf:

“The purpose of the adversarial system is to achieve just results.  All too often it is used by one party or the other to achieve something which is inconsistent with justice by taking advantage of the other side’s lack of resources or ignorance of relevant facts or opinions.  Expert evidence is one of the principal weapons used by litigators who adopt this approach.”[xii]

In the authors’ experience, practitioners from Asian countries that follow civil-law systems, including China, Japan and South Korea (whose legal systems are based primarily on the German legal code) also often believe that the inquisitorial system is much more time efficient, which in turn saves costs for both parties.  They often cite a comparison of the typical 5-day hearing in Hong Kong SAR, China as compared to the half-day hearings common in Chinese mainland litigation and arbitration.

Setting the efficiency argument to one side, regardless of whether the expert will be cross-examined by counsel or by an arbitrator directly, they should have a detailed knowledge of their own report and conclusions, and fully expect to be challenged on their underlying assumptions.  Perhaps a key difference between the two approaches (inquisitorial versus adversarial) is that it is all too obvious in the inquisitorial approach when an arbitrator finds an expert wanting.  In the authors’ experience, Chinese arbitrators have not shied away from directly criticising experts whom they consider have not delved sufficiently deeply into the underlying facts or have made unrealistic simplifying assumptions.

Hot-Tubbing (Aka Concurrent Evidence)

‘Hot-tubbing’ is a relatively recent development in the cross-examination of experts.  It involves the concurrent examination of experts led by the decision-maker, enabling simultaneous questioning and discussion on the issues.  In the authors’ experience, it is principally adopted in international arbitration and is seen less often in commercial litigation.

Views diverge as to whether this is an efficient or effective approach towards the cross-examination of experts. Advocates for hot-tubbing claim that it:

• Assists the decision-maker in understanding the differences between the experts and judging the relative strengths of the experts’ respective positions
  • Reduces the adversarial nature of traditional cross-examination and encourages experts to find areas of common ground
  • Enables weak or inconsistent arguments to be quickly challenged by the opposing expert (which may be difficult for counsel due to the technical nature of the concepts involved), thus improving the quality of the evidence presented at the hearing; and
  • Saves time and costs.

By contrast, its detractors argue that it:

• Requires significant input from the Tribunal, which must proactively guide the questioning of experts on the details of key issues.  It is therefore only effective if the Tribunal maintains control over the process, ensuring that both experts have equal opportunity to express their views
  • Can be less effective than traditional sequential cross-examination of experts where one expert is less dominant (for example due to a lack of experience, or cultural differences) and/or the experts are disinclined to cooperate; and
  • Removes control of the cross-examination of an opposing expert from counsel.  This may mean it is difficult for counsel to effectively put forward their own expert’s case to an opposing expert and to challenge the credentials or expertise of the opposing expert.

In the authors’ view, the efficacy of hot-tubbing is dependent on: (i) the nature of the issues that are subject to expert evidence; (ii) the ability of the Tribunal to sufficiently probe the experts on their evidence and manage the hot-tubbing process.

There is limited value in a technical debate between experts that does not clarify for the Tribunal the relevant issues and differences between the experts.  Similarly, hot-tubbing is not a test of the experts’ advocacy skills.  It works well in cases with discrete expert issues that can be handled separately but is less appropriate in cases where the experts’ underlying approaches are widely divergent.

Conclusion

Irrespective of the dispute resolution forum, an expert is required to provide an opinion on a specialist area that is: (i) relevant and necessary to determine the dispute; and (ii) outside the expertise of the Court or Tribunal.  The key skill of the expert is therefore communication – an ability to communicate complex and/or technical issues in a way that a lay audience can understand.

In both litigation and arbitration, the expert’s primary duty is to assist the Court / Tribunal.  Whilst there is a difference in the extent of guidance as to what this duty means in practice, experts in both fora should proceed on the widely accepted understanding that this requires impartiality, objectivity and independence from their instructing party.

Practically speaking, the main difference between litigation and arbitration from an expert’s perspective is that in arbitration, due to its inherent flexibility, several procedural milestones such as whether there will be joint reports or pre-hearing expert’s meetings are not known at the outset of the engagement.

The key differences between an expert’s role in litigation and arbitration are therefore procedural – rather than substantive – in nature. The litigation process is typically governed by strict procedural rules specific to the jurisdiction, which often extend to how the various aspects of the expert’s role – expert reports, meetings of experts and joint statements, and cross-examination at trial – are run.  By contrast, there are no regulatory frameworks applicable to experts in most institutional procedural rules and Tribunal members typically have authority to adopt procedural measures which they consider most appropriate in the circumstances.    

* This report was first published in Mealey’s Litigation Report: Artificial Intelligence.

[Editor’s Note: Nikki Coles is a Managing Director in London and Jon Nicklin a Senior Director in Shanghai with Alvarez & Marsal’s Disputes and Investigations practice.  Any commentary or opinions do not reflect the opinions of Alvarez & Marsal or LexisNexis®, Mealey Publications™. Copyright © 2025 by Nikki Coles and Jon Nicklin. Responses are welcome.]