A witness skilled in a field requiring particular expertise, whose opinion concerning an issue involving that field of expertise is exceptionally admissible evidence.
In NSW, expert witnesses are exempt from the operation of the opinion rule found at section 76 of the Evidence Act 1995, as per section 79 of the same Act. The opinion rule states that evidence of an opinion is not admissible to prove the existence of a fact. Expert witnesses however are allowed to give evidence of their opinions to prove the existence of a fact where they have specialised knowledge based on their training, study, or experience.
Expert witnesses are usually called by a party with the intent to either prove an element of their argument, or to disprove an element of the argument made by the opposing party. However, expert witnesses are expected to remain independent, and conduct themselves according to the Expert Witness Code of Conduct contained in Schedule 7 of the Uniform Civil Procedure Rules 2005.
‘Hot tubbing’ is the colloquial term for ‘concurrent expert evidence’ – the court practice of concurrently examining multiple expert witnesses. It involves engagement between the expert witnesses and advocates argue it forces further judge preparation, and can reduce time in the witness box, thereby lowering costs.