There are two broad categories of experts:
- Testifying Experts; and
- Consulting Experts.
The most significant difference between the two types of experts is that the testifying experts must be disclosed and render a written statement of their opinion, often called the expert’s report. A testifying expert may also be called to testify at trial or may be subpoenaed to oral deposition.
A consulting expert is hired to advise the attorneys about certain litigation-related issues, but not to testify. This means that the expert helps the attorney understand technical issues in the case, and can provide guidance during discovery, or making other strategic decisions with the testifying expert. Absent extraordinary circumstances, a consulting expert is not ordinarily subject to interrogatories or depositions. FRCP 26(b)(4)(D)(ii).
A testifying expert is used to present evidence and expertise in a specific subject matter at trial and during the pre-trial litigation stage. A testifying expert does more than provide advice; the expert typically prepares a written report of their opinion or a rebuttal of the opposition’s expert report. The expert also provides deposition testimony relating to their written opinion and may be called upon to testify at trial if necessary.
There is also a difference in the protections afforded to attorney-expert communications. The communications between a consulting expert and an attorney are typically protected, whereas any attorney-expert communications that relate to the required disclosures are subject to disclosure.