Concurrent Expert Evidence in the United States – Is There a Role for Hot Tubbing?

by Adam E. Butt

“Hot tubbing” is the colloquial name for a process of adducing and testing expert evidence which is more formally known as concurrent expert evidence. The method has been championed in Australia and is now used in other common law jurisdictions and in international arbitrations.


Australia’s version often involves two interrelated processes. First, there is a pre-trial joint expert conferencing (or conclave) phase, during which the parties’ experts meet to clarify the areas of agreement and/or disagreement between them, in order to produce a joint report. The second phase, if any, is the giving of concurrent evidence at trial in the “hot tub.” This part is moderated by the judge (usually the fact-finder), who can ask questions of the experts in order to enhance the fact-finding process for him or herself. The experts may also interact if they see a need to correct each other’s view, and cross-examination by counsel can still occur.


This model generally helps to yield benefits across a broad range of subject areas in Australia, through enhancing settlement prospects or improving the efficiency, quality and/or collegiality of the expert evidence process. In certain Australian jurisdictions, concurrent evidence has become the default rule. In the Federal Court it is a case management technique which is used in “appropriate circumstances.”


In so far as US judges are using the method, they tend to focus on the trial phase but the pre-trial part can also produce significant benefits. In Australia’s largest ever class action, Matthews v SPI Electricity Pty Ltd & Ors, which concerned major bushfires in Victoria, one of the joint expert reports enabled the summarising of some 2000 pages of expert reports into about 40 or 50 pages. This sort of efficiency is invaluable. Similarly, in the native title case Graham on behalf of the Ngadju People v Western Australia, the pre-trial expert conclave enabled the reaching of agreement on 21 out of 23 issues in dispute, which meant that cross-examination at the hearing was conducted in just 2 days during a 15 day hearing. By contrast, hearings in similar cases which pre-dated the concurrent evidence method have taken over 100 hearing days.


In the United States, judges have their own methods for enhancing the efficiency and accuracy of the evidence taking process. This includes requiring experts to present evidence “back to back,” holding “science days” in MDL litigation and appointing “expert panels” in pre-trial hearings.


But now United States judges are using hot tubbing too. Judge Woodlock (D. Mass) started using it after learning about the method from Australia’s Justice Heerey. Judge Zouhary (N.D. Ohio) started using it independently, only to later find out about the Australian method. Judge Weinstein (E.D. NY) started using hot tubbing after we first discussed the subject approximately 18 months ago.


Concurrent evidence has been used in toxics cases (e.g. Daubert hearing), a claims construction hearing, a class certification hearing and other civil matters. In general the method has not been seen as problematic in non-jury contexts; conversely, the judges and academics consulted or considered have endorsed the approach.


The jury setting, however, has elicited some different reactions. Judge Jones (D. Oregon) would avoid using hot tubbing in jury trials, believing it to be inappropriate for judges to inquire into or comment on expert evidence in front of jurors. Alternatively, Judges Hellerstein (S.D. NY), Weinstein, Woodlock and Zouhary do not consider that the jury is off limits but they have their certain qualifications. For example, Judge Woodock would need to be comfortable with who the experts were in order to use hot tubbing before a jury. Judge Zouhary would support using hot tubbing in jury cases where the expert evidence was complicated (it helps to comprehend such evidence), but would avoid using it in simpler matters. Judge Weinstein has actually now used hot tubbing in one jury trial, in a birthing case. Nevertheless, he states that he would intervene less in such settings, because his intervention may be demeaning to attorneys, the jury may give greater reliance to questions/positions put forward by the judge, and the concurrent presentation of evidence (cf. sequential presentation) may create complications in relation to burdens of proof and allowing attorneys to present their case.


Ultimately, hot tubbing appears to have a useful role to play in United States cases for the same reasons that the method is used in Australia and has gained traction elsewhere. It will be interesting to see the extent to which the method finds a place in the American context.





Sydney barrister and US attorney, Adam E. Butt, has undertaken research on this topic in a forthcoming article to be published in December: Concurrent Expert Evidence in U.S. Toxic Harms Cases and Civil Cases More Generally: Is There a Proper Role For “Hot Tubbing”?, 40 Houston J. Int’l L. 1 (2017).