Hot-tubbing – The Expert’s Friend?

Peter Caillard


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As Concurrent Expert Evidence (CEE), otherwise known as “hot tubbing”, becomes more popular as a modern approach to dispute resolution, it’s important to know what it means and why it’s used.

With this in mind, HKA’s Peter Caillard shares some reflections from a practising expert’s viewpoint, and asks: Is hot-tubbing the expert’s friend?

Concurrent Expert Evidence (CEE), sometimes referred to as witness conferencing, but colloquially known as “hot-tubbing”, is the practice whereby two or more experts at a hearing give their evidence concurrently. This enables simultaneous questioning and discussion on the key issues.

Traditionally, expert evidence involves each party’s experts providing examination-in-chief followed by cross-examination. Hot-tubbing is a more cooperative method.

Before the trial, experts issue written reports and engage in pre-trial meetings to identify areas of agreement and disagreement. At the trial, these experts are sworn in together, and a judge chairs a discussion between them, shaped by an agenda derived from a joint statement or court-approved issues of contention.

The main objective of hot-tubbing is to create an environment where experts engage in real-time discussions, allowing the court to focus on core issues. By having experts present their evidence concurrently, this process reduces the conventional adversarial combat between cross-examining counsel and experts.

In essence, hot-tubbing aims to put the experts on an equal footing, promoting discussions that reveal the strengths and weaknesses of their respective positions.

Context of Hot-tubbing (Concurrent Evidence)

In traditional dispute resolution, there is often a battle between opposing legal teams (who seek the best outcome for their respective clients) and the decision maker (whose objective is to arrive at a good decision). Decision makers – be they judges, sole arbitrators or arbitral panels – will wish to compress the experts into narrowing the issues.

Hot-tubbing contributes towards this process and should be seen as part of a continuum which includes preparing reports, meetings of experts, presentations, cross-examination, and hot-tubbing.

However, legal teams often fear a loss of control in a decision-maker led hot-tubbing session, and for this reason its use remains controversial. All of this can be seen in the context of a struggle for control of the agenda between legal teams. The experts and their opinions are at the centre of this struggle.

Background of Hot-tubbing (Concurrent Evidence)

Hot-tubbing had its origins in Australia in the 1970s. Its intention was to facilitate a discussion chaired by the decision-maker which encouraged cooperation between the experts towards agreement on key issues. Since then, its use has spread worldwide. In the UK, the Civil Procedural Rules Part 35 provide guidance for conducting the procedure.

The process can take varying forms in different jurisdictions. It can be used as an alternative to conventional cross-examination, or in addition to it. Questions may be put by each party’s counsel, the decision-maker, or more commonly, both. The process extends naturally from the preparation of a joint statement, whereby opposing experts have already discussed issues and recorded acknowledged areas of agreement and disagreement. Indeed, the joint statement is typically employed as the agenda for this part of the proceedings.

Hot-tubbing is usually led by the decision-maker, and this helps reinforce that the experts’ paramount duty is to the decision-maker, not their client.

Advantages of Hot-tubbing

There are a number of advantages to hot-tubbing that explain its increasing popularity.

The conventional cross-examination process can sometimes lead to frustration for experts facing aggressive questioning from counsel. This approach, aimed at discrediting the expert or diverting attention, poses challenges.

However, Concurrent Expert Evidence (CEE) offers an alternative. In the hot tub, questions are not solely posed by opposing counsel; the decision-maker takes an active role, focusing on understanding the expert’s position rather than attempting to catch them out. This dynamic creates a more sustainable and open environment for experts to present their opinions.

Some of the main advantages of hot-tubbing include:

  • Reduced Aggressiveness: Hot-tubbing minimises the aggressive nature often associated with conventional cross-examination, providing experts with a more constructive platform to present their views.
  • Decision-Maker’s Role: Questions in the hot tub are often posed by the decision-maker, concentrating on understanding the expert’s position and reasoning rather than attempting to discredit them.
  • Opportunity for Explanation: The hot-tubbing process offers experts greater opportunities to explain their opinions in-depth, compared to the narrow scope of traditional cross-examination.
  • Encouraging Common Ground: Hot-tubbing fosters an environment that encourages experts to find common ground, promoting collaboration over adversarial positions.
  • Building Credibility: Sitting in the hot tub alongside industry peers, experts are compelled to respond reasonably, enhancing their credibility through reasoned argumentation.
  • Risk Mitigation: The hot-tub setting reduces the risk of experts leaning towards critical opinions influenced by remote report writing or external criticisms.

While offering advantages such as reduced adversarial tones and enhanced cooperation, hot-tubbing also presents distinct challenges. These include:

  • Potential Dominance: Hot tubbing may encourage the dominance of one expert in the discussion, driven by their personality, experience, or eloquence. This dynamic could impact the equal contribution of all experts.
  • Limited Counsel Involvement: Counsel faces constraints in seeking their expert’s assistance while the other expert is speaking, as both experts are seated together. This may hinder the traditional back-and-forth collaboration between counsel and expert.
  • Shift in Preparation Focus: Time traditionally spent by counsel on preparing and probing experts for testimony must be redirected to hot-tubbing. This shift in preparation may introduce unfamiliar challenges for experts.
  • Risk of Over-Simplification: In the interest of time and comprehension, experts may face the risk of oversimplifying their explanations. Time constraints could contribute to discussions remaining at a superficial level.
  • Uncertain Time and Cost Savings: Contrary to expectations, hot-tubbing may not always result in time and cost savings compared to traditional cross-examination. Determining the scenarios where concurrent evidence is more appropriate poses a challenge.

The Expert’s Friend?

Hot-tubbing favours the expert who is well prepared, knows their subject, and who avoids the temptation to offer advocacy for their client’s case. Arguably it also favours the expert who is articulate and whose presentational skills are well-honed, although these qualities will not save the practitioner whose evidence is found wanting.

Furthermore, in cross-examination, counsel, however skilled and eloquent, suffers from one fundamental disadvantage. They are unlikely to possess the same level of subject matter understanding as the expert, and when questioning, may not always be able to react instantly to an answer which they do not fully comprehend. There is no-one to whisper in their ear with that killer follow-up question. In the hot-tub however, where other experts are on hand to provide instantaneous responses, there is less chance that flawed evidence will pass unchallenged or undetected. The hired gun is more easily exposed, as ill thought-through arguments will fall apart.

For many experts, the hot-tub experience is less daunting than cross-examination. The intensity of the spotlight is now shared. Critical thinking time is available while the other expert is speaking.

Most experts welcome the more relaxed and less formal atmosphere of the hot-tub, and the opportunity it presents to explain opinions rather than simply providing responses to opposing counsel’s carefully crafted questions. In the hot-tub there is nowhere to hide, but the expert who is focussed on assisting the decision-maker to reach the right decision does not need a hiding place.

The Decision-Maker’s Friend?

Hot-tubbing remains popular, and its use in dispute resolution is growing. It enables and encourages instantaneous discussion. Whereas in the hot-tub, an opinion proffered by one expert is quickly and easily referred to the other expert for a response, under cross-examination opposing experts may take the stand several days apart.

More importantly, joint discussion encourages experts to identify not only points of disparity but matters of agreement. This is of fundamental assistance to a hearing which is attempting to narrow down the issues.

There is little that pleases a decision-maker more than experts who have genuinely tried to find common ground! Although an independent approach cannot be forced upon experts, the format of the hot-tub facilitates and indeed encourages discussion and dialogue; the expert who acts as the hired gun is far more likely to be exposed than under conventional cross-examination.

Hot-Tubbing (Concurrent Evidence): The Verdict

A good expert has nothing to fear from hot-tubbing – indeed, they should relish the opportunity. An expert who has performed to their brief with diligence and remained cognisant of their primary duty to the decision-maker, will find that the hot-tub is their friend – indeed their credibility will shine through!

HKA is a global leader in expert services, serving clients worldwide in resolving disputes and complex technical issues. We are renowned for unparalleled expertise across various disciplines, from quantum analysis to commercial damages and forensic accounting

Our multidisciplinary approach extends to our expert witness and advisory services. We are the go-to solution for aid with arbitration, adjudication, mediation, and litigation.

Peter Caillard, a Chartered Civil Engineer with nearly four decades of experience in the construction industry, stands as a distinguished expert in the field. Holding a BSc (Hons) in Civil Engineering, he boasts professional memberships as a CEng, Eur Ing, FICE, and FCIHT. Peter’s extensive background includes the design and construction of highways, transportation, and infrastructure projects.

Throughout his illustrious career, Peter has managed projects across the globe, including in the UK, Europe, the Middle East, Africa, and North America. His expertise spans various aspects of design and construction, such as highway geometry, road pavement construction, drainage, earthworks, structures, public utilities, and materials testing. Beyond his design and managerial roles, Peter is well-versed in transport planning for both public infrastructure projects and private developments.

This publication presents the views, thoughts or opinions of the author and not necessarily those of HKA. Whilst we take every care to ensure the accuracy of this information at the time of publication, the content is not intended to deal with all aspects of the subject referred to, should not be relied upon and does not constitute advice of any kind. This publication is protected by copyright © 2024 HKA Global Ltd.


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