Checklist for Concurrent Expert Evidence


Assisting lawyers: preparing expert witnesses to give concurrent expert evidence

I have prepared a checklist for lawyers to consider when instructing experts to give concurrent expert evidence (commonly called “hot tubbing”) in court or at an arbitration. This guidance is based on my experience of giving concurrent expert evidence in arbitrations and in court.


• Always remember – the expert witness’s overriding duty is to assist the court/tribunal with their expertise.

• Draft the expert report in the knowledge that the judge/arbitrator may invite the expert with the apparently superior knowledge or more controversial position to take the lead in presenting the expert evidence.

• Expand the ‘joint statement’ by explaining or cross-referring all areas of disagreement to the expert reports as the judge/arbitrator will use this as the agenda.

• While preparing the joint statement with the other expert(s), the expert should think about how they will interact during the hot tub discussion. The expert must report to their instructing lawyer any concerns about their opposing expert’s experience or independence, which may render the hot tub unworkable.

• Check with the instructing lawyer the applicable court or arbitration rules and whether any modifications have been agreed with their opposite numbers and the judge/arbitrator, for example whether any cross-examination will take place before or only after the discussion.

• Establish the degree to which and the manner in which the judge/arbitrator has allowed experts to directly challenge the evidence of other experts in previous cases.

• Be ready with an opening statement setting out the overall position, where this may be allowed.

• The expert should plan how to respond to arguments that the other expert(s) may put.

• The expert should be encouraged to discuss any concerns with the instructing lawyer.

• Once in the hot tub, the expert must listen attentively to the other expert’s arguments and avoid the danger of simply being carried along by their presentation.

• In this less structured environment the expert may need to respond to a very persuasive, confident or assertive expert, but without becoming an advocate for their own client’s case. 

• Consider asking the expert to provide an assistant to assist the party’s legal team during cross examination.

This checklist is based on guidance I prepared for members of my professional body, the Institute of Chartered Accountants in England and Wales. 

In future blogs I shall explain my experience of giving expert evidence in more detail.

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Charles Lazarevic

20 April 2020

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