The Adjudication of Expert Witness Testimony: A Comparative Analysis

11 Min Read By: Susan W. Lanham, Casey W. Baker

In the intricate world of legal proceedings, courts globally depend heavily on evidence and testimonies to render fair and informed decisions. A critical component of this process is the role of expert witnesses, whose specialized knowledge and insights are invaluable in helping courts understand complex issues that lie beyond the purview of lay understanding. However, the criteria for determining the credibility of an expert’s opinion and the standards for who qualifies as an expert witness vary significantly across different countries. In this article, we embark on a comparative analysis of how nations like the United States, Australia, Brazil, Canada, Israel, Japan, South Africa, and the United Kingdom approach these pivotal questions.

Our exploration of expert witness standards comes at a particularly pivotal moment, as legal systems around the world are actively updating their frameworks to address new challenges and complexities. A prime example of this evolution is the recent modification to the Federal Rules of Evidence, specifically Rule 702, in the United States.[1] These changes, which officially took effect on December 1, 2023, have sparked significant debate and discussion within the legal community.[2] The amendments to Rule 702 are aimed at refining the criteria for admissibility of expert testimony, with the goal of ensuring that such testimonies are not only relevant but also reliably grounded in sound scientific and technical principles.[3] This development underscores the ongoing efforts to balance the need for reliable and credible expert testimonies with the principles of fairness and justice that are foundational to the legal system.

By examining the practices employed in various countries, we aim to uncover common trends and distinctive approaches that each nation adopts. This exploration reviews the underlying reasons for these diverse rules, considering each country’s unique cultural, historical, and legal contexts. Our objective is to paint a comprehensive global picture of expert witness regulations, extracting valuable insights that could potentially inform and enhance these systems universally. Through this study, we hope to contribute to the ongoing discourse on refining the standards and practices surrounding expert witness testimonies, ensuring that they continue to serve the cause of justice effectively in different legal landscapes.


United States: The Judge as Gatekeeper

In the United States, Rule 702 of the Federal Rules of Evidence places the judge in the role of a gatekeeper, responsible for assessing expert witnesses’ qualifications and the reliability of their methodology. Judges must ensure that the testimony meets four criteria: relevance to the case, sufficiency of facts and data, reliability of principles and methods, and the application of methods to the facts of the case.[4]

While this approach aims to standardize expert testimony, it has its limitations. Judges are not always familiar with the methodologies employed in specialized fields, which may result in errors in judgment.[5]

Furthermore, amended Rule 702 expressly places the burden of proving admissibility on the proponent of the testimony. Previously, many courts in the United States presumed admissibility of expert opinion, leaving it to juries to weigh the merits of the witness testimony. Under the amended rule, admissibility must be determined prior to the presentation to the jury. To rebut challenges by the opposition, a litigator must be sufficiently comfortable with the methodologies and technical aspects of the expert evidence.[6]

Australia: The ‘Hot Tubbing’ Technique

Australia is renowned for its “hot tubbing” method, officially known as concurrent expert evidence.[7] This unique approach brings expert witnesses from opposing sides together in the courtroom to discuss their methodologies and answer questions simultaneously.[8] This interactive setting allows for direct comparison and a dynamic dialogue, highlighting the strengths and weaknesses of each expert’s approach.[9] It’s a less formal yet effective method that facilitates robust discussions, aiding judges in making well-informed decisions.[10]

Brazil: An Inquisitorial Model

Brazil employs an inquisitorial model that persists despite reform efforts that sought to make it more adversarial.[11] In this setup, judges have a proactive role and can request expert examinations.[12] Parties may not cross-examine directly; instead, the judge has authority to filter questions in pursuit of truth.[13] While judges do not solely decide on the admissibility of expert testimony, they play an influential role in weighing the credibility and methodology of the evidence presented.

Canada: A Balanced Approach

Canadian courts follow a somewhat flexible approach regarding expert witnesses.[14] Known as the Mohan criteria, the Canadian system examines relevance, necessity, absence of an exclusionary rule, and the qualifications of the expert.[15] In particular, Canadian courts emphasize the importance of objectivity and absence of bias in experts, but these courts tend to be more accommodating than their American counterparts.[16]

Under the Canadian system, the initial question of admissibility requires the expert to testify under oath or to attest that his or her primary duty is to the court—not the party retaining the expert.[17] Once this threshold is met, the Canadian model relies on the adversarial system and cross-examination to challenge the expert’s ability to fulfill this duty, as well as to uncover any flaws in methodology or qualifications that would indicate that the risk of allowing the evidence to be admitted outweighs the benefits of admission.[18]

Israel: An Adversarial Approach

Israel adopts an adversarial system like that of the United States, but with less emphasis on the judge as a “gatekeeper.” All judicial proceedings in Israel are bench trials.[19] Thus, there is less need to vet expert witness testimony prior to presentation to the fact finders. The court has full discretion concerning whether or not to accept the expert’s conclusions.[20]

Parties are largely free to introduce expert witnesses, who are then subjected to cross-examination during trial.[21] The focus here is on the in-trial adversarial process to vet the reliability of the expert’s methodology rather than pretrial judicial assessment. In addition, the court has authority to appoint its own experts.[22]

Japan: Judges and Advisory Experts

Japan uses a combination of judge-centered and expert-guided approaches. District courts are often divided into multiple divisions, with disputes being assigned to a particular division where the judge has relevant expertise.[23] If the topic is complex and beyond a judge’s understanding, advisory experts may be appointed to clarify technical aspects.[24]

Experts are appointed by the court at the request of a party but can be challenged by any opposing party.[25] These advisers provide independent advice to the court, subject to cross-examination.[26] The goal is to help the judge to comprehend the methodology, albeit leaving the ultimate decision to the judge.[27]

South Africa: Adversarial with a Twist

South Africa follows an adversarial system, where the admissibility of expert testimony largely depends on the qualifications of the witness and the relevance of the testimony to the case at hand.[28] What makes South Africa distinct is the lack of reliance on expert testimony.[29] Rather, South African courts see expert testimony as one bit of evidence in a narrative of events.[30] Thus, litigants should take care to emphasize the expert’s professional integrity to convince the fact finders of the value of the testimony.[31] Likewise, clarity of the expert’s presentation is also important in helping craft the narrative most helpful to the party’s interests.[32]

United Kingdom: A Less Stringent Approach

The UK takes a less stringent approach than the United States. The courts generally allow expert witness testimony unless there is a clear reason to doubt the expert’s qualifications or methodology.[33] However, the legal teams on both sides usually subject the expert’s testimony to intense scrutiny through cross-examination. If an expert is found to lack credibility or their methodology is questionable, it can be challenged and discredited in court.[34] This system places more faith in the adversarial process than in the judge’s discretion to ensure reliable expert testimony.

Merits and Limitations

Different countries have adopted varied approaches based on their legal traditions, cultural norms, and particular needs. It is not possible to determine which country most effectively vets expert witness testimony. Each method has its merits and limitations. Below are some aspects to consider.


The US system aims for a high degree of standardization through Rule 702 of the Federal Rules of Evidence. This approach seeks to filter out unreliable methodologies before they can be presented in court. However, this system places a heavy burden on judges and litigators, who may not be experts in specialized fields.

Adversarial Scrutiny

The UK and Israel rely heavily on the adversarial system and believe that rigorous cross-examination will expose any weaknesses in an expert’s testimony. While this allows for a broader range of expert input, it may also permit less reliable testimony to enter into evidence if not adequately challenged.

Collaborative Scrutiny

Australia’s “hot tubbing” technique provides a unique platform for collaborative scrutiny. It enables judges to compare methodologies directly and question experts in real time. This system, however, requires experts who can think on their feet and engage in academic debate, which is not a skill that every expert possesses.


Canada’s Mohan criteria offer a flexible framework for assessing expert testimony, balancing both judge-driven and adversarial elements. However, this flexibility might also lead to inconsistencies in how expert testimony is evaluated.

Pursuit of Truth

Brazil’s inquisitorial model leaves questioning of experts to the judge, in an independent pursuit of truth. While this approach may reduce partisan spin, it also leaves open the real risk of judicial bias and possible corruption.

Ethical Responsibility

South Africa’s system places a high premium on the ethical responsibility of the expert, adding an additional layer of vetting that focuses on integrity rather than just qualifications or methodology.

Specialized Assistance

Japan’s use of advisory experts can be seen as a way to bridge the knowledge gap for judges, though it adds another layer of complexity.

Cultural and Legal Factors

It’s important to note that what works well in one country may not necessarily be effective in another due to various factors, including legal traditions, the role of the judiciary, and cultural attitudes toward authority and expertise.


Expert witness testimonies are a cornerstone of justice systems globally, providing critical insights that can sway judicial outcomes.

Our exploration reveals how various countries have tailored their approaches to expert witness testimonies, each reflecting a unique blend of cultural, legal, and historical contexts. From the structured approach of the US system to Australia’s interactive “hot tubbing” method to South Africa’s focus on ethical integrity, these diverse methodologies are custom designed to suit the specific needs of each jurisdiction.

However, one constant in this varied landscape is the ongoing evolution of these systems. As we navigate through an ever-changing world marked by advancements in knowledge, technology, and shifting societal values, the rules and practices governing expert witnesses are also adapting. This adaptability reflects the dynamic nature of justice and the relentless effort to strike a balance between reliability and fairness in legal proceedings.

This comparative study highlights the importance of international collaboration and the exchange of best practices. By gaining insights into the varied approaches adopted by judiciaries around the world, we can continually refine and enhance our own systems. This is particularly vital in today’s fast-paced era, where the accuracy and credibility of expert testimonies are more critical than ever. As we move forward, ensuring that expert witnesses remain a dependable and integral part of the legal process will be key to upholding the principles of justice and fairness in an increasingly complex and interconnected world.

  1. Hon. Patrick J. Schlitz, Jud. Conf. of the U.S., Committee on Rules of Practice and Procedure: Report of the Advisory Committee on Evidence Rules 5–8 (2022).

  2. See, e.g., Kristen M. Bush & Kayla M. Kuhn, Proposed Amendments to Federal Discovery Rule of Evidence 702 and Their Impact on Expert Discovery, Brief, Winter 2023, at 54.

  3. Ayako Russell & Jay Thomas, Proposed Changes to Federal Rule of Evidence on Expert Witness Testimony, Glob. Investigations & Compliance Rev., Apr. 10, 2023.

  4. Fed. R. Evid. 702.

  5. Bush & Kuhn, supra note 2.

  6. Russell & Thomas, supra note 3.

  7. Peter Caillard, Hot-Tubbing—The Experts Friend?, HKA Glob. Ltd., Feb. 14, 2023.

  8. Id.

  9. Id.

  10. Id.

  11. Ludmila Ribeiro et al., Decision-Making in an Inquisitorial System: Lessons from Brazil, 56 L. & Soc. Rev. 101, 105 (2022).

  12. Id.

  13. Id.

  14. See Brad D. Booth et al., Lessons from Canadian Courts for All Expert Witnesses, J. Am. Acad. Psychiatry L., May 16, 2019, at 1.

  15. Id. at 2–3.

  16. Id. at 6–7.

  17. White Burgess Langille Inman v. Abbott & Haliburton Co., [2015] 2 S.C.R. 182, para. 46 (Can.).

  18. Id. paras. 47–48.

  19. Sivon Wulkan-Avisar & Akiva Fund, Guide to Litigation in Israel: Israeli Legal System and Service of Process, Lexology, Apr. 18, 2023.

  20. David Fohrer, Found. Int’l Ass’n Def. Couns., Survey of International Litigation Procedures: A Reference Guide: Israel § 14 (2014).

  21. Id. § 9.

  22. Id. § 15.

  23. Craig I. Celniker et al., Litigation and Enforcement in Japan: Overview, Thomson Reuters Prac. L., 2016, § 3.

  24. Id. § 19.

  25. Id.

  26. Id.

  27. Id.

  28. Lirieka Meintjes-Van Der Walt, The Proof of the Pudding: The Presentation and Proof of Expert Evidence in South Africa, 47 J. Afr. L. 88, 94–99 (2003).

  29. Id. at 89.

  30. Id. at 103–04.

  31. Id. at 92.

  32. Id. at 95–99.

  33. See Crown Prosecution Serv., Prosecution Guidance: Expert Evidence (Nov. 20, 2023).

  34. Id.

By: Susan W. Lanham, Casey W. Baker


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