If the witness needs to testify in court, the privilege is no longer protected. The expert witness’s identity and nearly all documents used to prepare the testimony will become discoverable. Usually an experienced lawyer will advise the expert not to take notes on documents because all of the notes will be available to the other party.
An expert testifying in a United States federal court must satisfy the requirements of Fed. R. Evid. 702.Generally, under Rule 702, an expert is a person with “scientific, technical, or other specialized knowledge” who can “assist the trier of fact,” which is typically a jury. A witness who is being offered as an expert must first establish his or her competency in the relevant field through an examination of his or her credentials. The opposing attorney is permitted to conduct a voir dire of the witness in order to challenge that witness’ qualifications. If qualified by the court, then the expert may testify “in the form of an opinion or otherwise” so long as: “(1) the testimony is based upon sufficient facts or data, (2) the testimony is the product of reliable principles and methods, and (3) the witness has applied the principles and methods reliably to the facts of the case.”
Although experts can testify in any case in which their expertise is relevant, criminal cases are more likely to use forensic scientists or forensic psychologists, whereas civil cases, such as personal injury, may use forensic engineers, forensic accountants, employment consultants or care experts. Senior physicians – UK, Ireland, and Commonwealth consultants, U.S. attending physicians – are frequently used in both the civil and criminal courts.
The Federal Court of Australia has issued guidelines for experts appearing in Australian courts. This covers the format of the expert’s written testimony as well as their behavior in court. Similar procedures apply in non-court forums, such as the Australian Human Rights and Equal Opportunity Commission.