Efficiency of ‘hot tub’ process

Procedure – Children – Four medical expert witnesses ordered to confer (to prepare a list of the issues and as to which the experts agreed and disagreed) then to give concurrent evidence (“in the hot tub”) – Relevant principles

In Ashdown & Markin (No 2) [2026] FedCFamC1F 164 (16 March 2026), Wilson J considered the use of expert evidence in parenting proceedings. The mother alleged family violence by the father and also alleged that he suffered from various psychological conditions ([6]).

The proceedings involved expert evidence from three psychologists and one psychiatrist. The conclusions reached by those experts differed significantly ([6]).

After considering the amount of time sequential evidence from each of the experts would take, His Honour asked counsel whether there would be agreement for the evidence to be heard concurrently ([9]).

The Court said (from [10]):

“This court has been slow to embrace the concept of concurrent evidence. Conversely, in the Federal Court of Australia concurrent evidence is commonplace. …

[11] No fixed method of the adducing of concurrent evidence enjoys universal application. … One size does not fit all. That said, in this court general principles of procedural fairness apply requiring all counsel to be given a fair opportunity to question all experts. …

[12] Several days were proposed for the experts to give their evidence by conventional means. … As with any cross-examination, once a witness is excused from giving further evidence after that witness’s evidence is completed, he or she can only be recalled by agreement or by leave… Unless leave is given in that scenario to recall the first witness and then put to him or her the proposition advanced by the subsequent expert, the judge is left at risk of being misinformed about some aspect of the expert evidence or worse, about the totality of the expert evidence. That is wholly undesirable. It should be avoided wherever possible.

[13] The hot tub operates in such manner as to avoid the risks associated with that scenario.

( … )

[26] The hot tub concluded by the luncheon adjournment on 13 March 2026. The entirety of the experts’ evidence was concluded in one stage within three hours, thereby demonstrating the efficiency of the hot tub process.”