Expert Witness Disclosure Rules: Consulting vs. Testifying Experts

Christine Funk

Written by
— Updated on April 27, 2022

Expert Witness Disclosure Rules: Consulting vs. Testifying Experts


If you are using an expert in your case, you may or may not, be required to disclose the witness. However, the rules for disclosure of expert witnesses differ depending on the type of expert you elect to retain. Because of this variation, it is a good idea to put some thought into what kind of expert best suits your client’s needs.  Will your expert merely consult?  Or do you plan to have them testify at trial?  Additionally, consideration must be given to jurisdiction. Finally, even when in the same jurisdiction, the rules may be different for civil versus criminal cases.

Deciding Which Type of Expert You Need

It’s unlikely you will know for certain if you are going to put your expert on the stand in either a civil or criminal case. It is entirely possible that, after reviewing the file, your expert will conclude the other side’s expert got it right, or that the other side’s expert came to the right conclusion, even though they relied on incorrect data or an improper technique to arrive at their conclusion. In either event, your expert won’t be testifying.  However, that doesn’t render them useless.

Proceed With Caution – You Can’t Un-Ring the Bell

In both criminal and civil proceedings in federal court, if you decide to consult with an expert, and later decide the expert will testify, you can convert the expert from a consulting expert to a testifying expert by disclosing certain things, to be discussed in detail below.  

If, on the other hand, you disclose your expert’s identity at the outset and then discover your expert will not make a good witness for your client’s case, you can’t un-ring that bell.  The other side will know you have consulted with an expert and, unless they have only been out of law school for five minutes, they will know exactly why your expert isn’t testifying.  Depending on the jurisdiction, the other side may be able to call your expert as a witness supporting their theory of the case. The last thing you want to do is create another credible witness for the other side.

The Consulting Expert

A consulting expert starts by reviewing the data.  They provide the attorney with information about their conclusions, and, where applicable, the conclusions of the other expert.  If the consulting expert has helpful information for your side, you may decide they will become a testifying expert.  When this comes to pass, federal law requires certain things in the form of disclosure.  If, on the other hand, you decide they will not testify, federal law doesn’t require disclosure before trial in either civil or criminal cases.

Even though a consulting expert doesn’t testify, they can still help you poke holes in the other side’s theory, methods, or even assist in mounting a challenge to the expert him or herself.  A consulting expert can point you to studies published in peer reviewed journals that establish a theory has been debunked or to literature establishing a method has been replaced with one that is more efficient. Based on their involvement in the community, they may also know about some professional missteps the expert has made which may be useful for impeachment. Having an expert in the front row while the expert for the other side testifies can also serve two functions for counsel: 1) keep the other expert more honest, and 2)  provide a safety net for the attorney who may otherwise be lost should the testifying expert go off on an unanticipated tangent.

When You Decide Your Expert Will Testify

When you decide your expert will testify, you have a legal obligation to disclose this to the other side.

Experts in Federal Civil Cases

In federal court in civil cases, the duty to disclose is addressed in Federal Rule of Civil Procedure 26, “Duty to Disclose.”  State courts may have different rules about what, when, and how information should be disclosed.  In federal court, however, the expert must be disclosed 90 days before the trial date, unless the judge has set another timeline.  Fed.R.Civ.Pro. 26 (a)(2) requires disclosure if the expert will present evidence under Federal Rule of Evidence 702, 703, or 705.  The disclosure must include a report, written by the witness, which includes:

  •         A comprehensive statement, covering all of the opinions the witness intends to express;
  •         The basis and reasons for those opinions;
  •         The facts the witness considered when forming their opinions;
  •         Any exhibits the witness intends to use to support, summarize, or otherwise advance the testimony;
  •         Expert qualifications, which include all publications authored by the expert over the past 1 years;
  •         A list of all cases wherein the witness testified during the prior four years, either in a trial or during a deposition; and finally,
  •         An accounting of the witness’s compensation, both for the review of the file, trial preparation, and testimony.

Expert Witness Testimony as Rebuttal

In the federal system, when an expert intends to provide rebuttal testimony, the timeline for disclosure differs. In that case, the disclosure must be made within 30 days of receiving the opinion from the other side.

Work Product

The federal civil rule protects work product of experts including drafts of the expert’s reports, as well as communications, both oral and written, between the attorney and the expert.  Although there are a few exceptions to this rule, conversations about compensation are always discoverable and must be disclosed.  Additionally, the facts and circumstances of the case, which the attorney provided to the expert to formulate an opinion also must be disclosed, as detailed above. Any assumptions the attorney provided which the expert relied upon in drawing their conclusion must also be disclosed.

This approach allows an attorney to have meaningful discussions with an expert, exploring any and all possible theories of the case, without fear the other side will learn of, and exploit this information to the detriment of the client.  At the same time, by disclosing a detailed list of the information the expert relied on in drawing their conclusions, the other side is afforded a clear understanding of what the expert did (or, in some cases, did not) consider.

Experts in Federal Criminal Cases

Federal Rule of Criminal Procedure 16 (a) (1) (G) discusses expert witnesses in criminal cases.  If the defendant requests it, the government must provide written summaries of any testimony the government plans on using under either Rule 702, 703, or 705 of the Federal Rules of Evidence in its case in chief.  The government enjoys reciprocal discovery if the defendant has an expert and the defendant has been provided information about the government’s expert.

The written disclosure must include the witness’s opinions, the reasons and basis for each of their opinions, and the qualifications of the witness.  

State Court Rules

Different states, of course, have different rules governing discovery of experts and expert testimony.  While some states follow the federal rule, many do not. Pennsylvania, for example, requires the use of interrogatories to discover the identity of any experts, the subject matter they intend to testify to, the substance of the facts and opinions the expert will testify to, and a summary for the basis of the opinion.  Pennsylvania’s rules provide similar protections for non-testifying witnesses. Tennessee has a similar rule. Reports are not required.  Oregon, on the other hand, does not require the disclosure of either the name nor the substance of an expert’s testimony in advance of trial.  

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