The Importance of Impartiality of Expert Witnesses in International Arbitration and Litigation 

As published in Lexology on 11 April 2025.

What is an Expert Witness

An expert witness is called upon to provide an independent opinion based on expertise in a particular field. We do not advocate a party’s case; our duty is to the tribunal or court. This principle is encapsulated in the International Bar Association (IBA) Rules on the Taking of Evidence in International Arbitration, addressing the independence of experts in Article 5, which explicitly requires experts to act independently and disclose any conflicts of interest. Specifically, the rules mandate that expert reports include a declaration of independence and disclose any relationships that might affect the expert’s impartiality.¹

Legal Requirements of Impartiality

Common Law Jurisdictions

In common law systems, the courts have emphasised the importance of impartiality in expert testimony. The Ikarian Reefer ² articulated key principles governing expert evidence. Justice Cresswell underscored that the duties and responsibilities of expert witnesses in civil cases include:

1. Independent assistance to the court by way of objective, unbiased opinion.
2. Stating the facts or assumptions upon which their opinion is based and should not omit material facts that could detract from their concluded opinion.
3. Making it clear when a question falls outside their expertise.³

The Civil Justice Council (UK) issued updated guidance in August 2014, Practice Direction 35 and ‘Guidance for the instruction of experts in civil claims’.⁴

Civil Law Jurisdictions

In civil law systems, the appointment of experts is often court-driven, inherently emphasising neutrality. For instance, under the French Code of Civil Procedure (Article 237), “The commissioned technician must carry out his mission conscientiously, objectively and impartially.” The court-appointed experts are explicitly required to act with impartiality. The code stipulates that experts must provide objective and unbiased opinions, and any party to the proceedings can challenge an expert if there is a suspicion of bias or conflict of interest. This reinforces the principle of neutrality inherent in the civil law tradition.⁵

International Arbitration

The IBA Rules⁶, CIARB protocols⁷ and the UNCITRAL Arbitration Rules⁸ highlight the need for expert impartiality. Article 5 of the IBA Rules stipulates that expert reports must include a statement of independence, affirming that the opinions expressed are uninfluenced by the appointing party.

Case Law Demonstrating the Consequences of Bias

National Justice Compania Naviera SA v. Prudential Assurance Co Ltd (“The Ikarian Reefer”)

This case serves as a cornerstone for understanding the role of expert witnesses in common law jurisdictions. The court excluded portions of an expert’s testimony, noting that the expert had aligned too closely with the appointing party’s interests, thereby undermining their impartiality.⁹

R (Factortame Ltd) v. Secretary of State for Transport (No. 2) [1991] AC 603

In this case, the House of Lords considered the role of expert witnesses in addressing technical evidence. The court emphasized that experts must serve the administration of justice rather than the interests of the party instructing them.

Methanex Corporation v. United States of America

This arbitration under NAFTA highlighted the tribunal’s concerns about the credibility of an expert’s testimony due to perceived bias. The tribunal gave diminished weight to the expert’s evidence, reinforcing the necessity for neutrality.

Insights from Related Articles

I have reviewed comparable articles that provide further insights into the challenges and recommendations for maintaining expert witness impartiality:

1. “Expert Evidence in International Arbitration: Common Criticisms and Innovative Solutions” (K&L Gates): This article highlights the frequent criticisms of expert evidence, including undue influence by appointing parties, and proposes solutions such as tribunal-appointed experts and stricter disclosure requirements.¹⁰
2. “Expert Evidence in International Arbitration” (Cleary Gottlieb): This piece emphasizes the necessity for impartial and unbiased opinions, uninfluenced by the pressures of the dispute resolution process.¹¹
3. “Reliability of Expert Evidence in International Disputes” (University of Michigan Law School): This scholarly article discusses the discretion of adjudicators in evaluating expert testimony and the importance of impartiality in preserving its reliability.¹²
4. “The Use of Experts in International Arbitration” (Charles Russell Speechlys): This article focuses on the selection process for party-appointed experts and stresses measures to ensure impartiality.¹³

There does seem to be a broader discourse on ensuring that neutrality in expert testimony, offering valuable perspectives and solutions to common challenges, are mandatory.

Practical Challenges and Recommendations

Despite the available legal frameworks and industry guidelines, challenges persist on a regular basis. Party-appointed experts may face subconscious biases, given their engagement by one side of the dispute. This leads to the arbitrators, counsels, and courts to scrutinising expert evidence critically, particularly where it appears overly aligned with a party’s case.

Recommendations for Maintaining Impartiality:

1. Experts should engage in ongoing training and certification to stay updated with evolving industry standards and best practices, ensuring their knowledge remains current and reliable.
2. Experts should clearly outline the methodologies and data used in forming their opinions, providing transparency that allows for independent verification and reduces the risk of bias.
3. Establishing and adhering to a code of ethics that provides a framework for maintaining impartiality and professional conduct.
4. Experts should seek diverse project experience across different sectors and clients, reducing the risk of unconscious bias that may develop from repeated engagements with similar parties.
5. If allowed, permit external audits or third-party reviews of expert findings, providing an additional layer of objectivity and confidence in the impartiality of the opinion provided.
6. Difficult to implement but aim to work with a balanced mix of claimants and respondents over time, demonstrating a lack of consistent bias toward one side.
7. Ensuring that the instructions are clear and unbiased without influence or pressure to favour a particular outcome.
8. Self-assessment of own reports and performance to identify potential patterns of bias and take corrective measures where necessary.
9. “If in doubt, declare.” Full disclosure of any prior relationships with the parties or counsel provides clarity and avoids potential conflicts of interest.
10. The tribunal appointed expert may mitigate concerns about partiality.
11. Subjecting expert reports to peer review.
12. Rigorous cross-examination remains a critical tool for evaluating an expert’s impartiality and the robustness of their opinions.

These measures collectively strengthen the impartiality, credibility, and professionalism of expert advice, enhancing trust in the integrity of their recommendations.

Conclusion

The impartiality of expert witnesses is a cornerstone of fair dispute resolution in international arbitration and litigation. As seen in cases like The Ikarian Reefer and Methanex Corporation v. United States of America, partiality not only undermines the expert’s credibility but also jeopardises the integrity of the adjudicative process. By adhering to established principles and implementing practical safeguards, the legal community can ensure that expert testimony remains a reliable and impartial aid to justice.

About the Author

References

1. Article 5 Party-Appointed Experts, IBA Rules on the Taking of Evidence in International Arbitration, adopted by a resolution of the IBA Council 29 May 2010, (International Bar Association, 17 December 2020) https://www.ibanet.org/MediaHandler?id=def0807b-9fec-43ef-b624-f2cb2af7cf7b accessed 16 December 2024 ↩︎
2. National Justice Compania Naviera SA v Prudential Assurance Co Ltd: The Ikarian Reefer 2 Lloyd’s Rep 68 Commercial Court [1993]; 1 Lloyd’s Rep 455, CA [1995]  ↩︎
3. The Ikarian Reefer, (RICS ISURV, 2016) https://www.isurv.com/directory_record/3794/national_justice_compania_naviera_sa_v_prudential_assurance_co_ltd_the_ikarian_reefer accessed 19 December 2024  ↩︎
4. Civil Procedure Rules, Part 35.3 – Experts – overriding duty to the court https://www.justice.gov.uk/courts/procedure-rules/civil/rules/part35#IDASLICC accessed 20 December 2024  ↩︎
5. Article 237 of the French Code of Civil Procedure, https://french-business-law.com/french-legislation-art/article-237-of-the-french-code-of-civil-procedure/ accessed 20 December 2024  ↩︎
6. IBA Rules on the Taking of Evidence in International Arbitration, (International Bar Association, 2020) https://www.ibanet.org/MediaHandler?id=def0807b-9fec-43ef-b624-f2cb2af7cf7b accessed 20 December 2024  ↩︎
7. Party-appointed and Tribunal appointed Experts, International Arbitration Practice Guidelines, (Chartered Institute of Arbitrators, 2016) https://www.ciarb.org/media/zvijl3kx/7-party-appointed-and-tribunal-appointed-expert-witnesses-in-international-arbitration-2015.pdf accessed 20 December 2024  ↩︎
8. UNCITRAL Arbitration Rules (2021), UNCITRAL Expedited Arbitration Rules, UNCITRAL Rules on Transparency in Treaty-based Investor-State Arbitration https://uncitral.un.org/sites/uncitral.un.org/files/media-documents/uncitral/en/21-07996_expedited-arbitration-e-ebook.pdf accessed 20 December 2024  ↩︎
9. The Ikarian Reefer, (RICS ISURV, 2016) https://www.isurv.com/directory_record/3794/national_justice_compania_naviera_sa_v_prudential_assurance_co_ltd_the_ikarian_reefer accessed 19 December 2024 ↩︎
10. Ian Meredith, Louise Bond, “Expert Evidence in International Arbitration: Common Criticisms and Innovative Solutions”, (Arbitration World Alert, 24 August 2021) https://epc.klgates.com/getStdDoc.aspx?MediaID=135004 accessed 18 December 2024  ↩︎
11. Thomson Reuters, Expert evidence in international arbitration, (Practical Law Arbitration, 2020) https://www.clearygottlieb.com/-/media/files/evidence-in-international-arbitration-83822039-pdf.pdf accessed 18 December 2024  ↩︎
12. Matthew W. Swinehart, “Reliability of Expert Evidence in International Disputes”, (2017) Michigan Journal of International Law Volume 38 Issue 2, available at https://repository.law.umich.edu/cgi/viewcontent.cgi?article=1489&context=mjil (accessed 20 Dec 2024)  ↩︎
13. The Use of Experts in International Arbitration, (Charles Russell Speechlys, 04 June 2024) https://www.charlesrussellspeechlys.com/en/insights/expert-insights/dispute-resolution/2024/the-use-of-experts-in-international-arbitration/ accessed 21 December 2024  ↩︎