Many lawyers use the terms “supplemental expert” and “rebuttal expert” interchangeably, but, according to the Discovery Act, they are very different. A supplemental expert is one that was disclosed twenty days after experts have been disclosed and is pursuant to Code of Civil Procedure section 2034.280 and is allowed to provide expert testimony. However, a rebuttal expert’s testimony is limited to rebutting or contradicting an opponent’s expert’s “foundational facts” that form the basis of their opinion.
A party may call as a witness at trial an expert not previously designated by that party if either of the following conditions is satisfied:
(a) That expert has been designated by another party and has thereafter been deposed under Article 3 (commencing with Section 2034.410).
(b) That expert is called as a witness to impeach the testimony of an expert witness offered by any other party at the trial. This impeachment may include testimony to the falsity or nonexistence of any fact used as the foundation for any opinion by any other party’s expert witness, but may not include testimony that contradicts the opinion.
The use and limitations of a rebuttal expert are best explained in the cases of Kennemur v. State of California (1982) 133 Cal.App.3d 907 and Fish v. Guevara (1993) 12 CA4th 142. Here are the pertinent points the Courts of Appeals makes in each case:
In Kennemur, the Court of Appeal stated “when it comes to impeaching expert witnesses, the distinction between an opinion and a foundational fact–though arbitrary–must be made. . . . In many cases, the ultimate opinion of the expert is based on a series of underlying opinions. Thus, rather than broadly construing what a foundational ‘fact’ is, the term should be strictly construed by the trial court to prevent a party from offering a contrary opinion of his expert under the guise of impeachment.” (Kennemur at 904)
The rationale for the rebuttal witness statute is that any testimony from any source should be admissible on the veracity of the opposing expert’s opinion. Therefore, even an undisclosed expert may be permitted to contradict facts upon which opposing experts based their opinion upon. If opposing party’s experts foundational facts are wrong, then their opinions may not be worthy of belief by the trier of fact. (Cal. Prac Guide: Civil Procedure Before Trial (TRG 2021) 8:1729 citing Kennemur at 924-925)
The court stressed that an undisclosed expert may not go further and offer a conflicting opinion or to “rebut” that given by the opposing experts. (Kennemur at 907)
In Fish, the Court of Appeal stated that “[a] party may call as a witness at trial an expert not previously designated by that party if . . . that expert is called as a witness to impeach the testimony of an expert witness offered by any other party at the trial. This impeachment may include testimony to the falsity or nonexistence of any fact used as the foundation for any opinion by any other party’s expert witness but may not include testimony that contradicts the opinion.” (now §2034.310(b). Hence, an undisclosed expert may testify to facts which contradict the factual basis for the opinions of other experts but may not give opinion testimony which contradicts the opinions of other experts.” (Fish at 145)
For example, “[a]n undisclosed expert may testify that the foundational facts were different than the opposing expert supposed (e.g., speed of the car, patient’s prior medical history, etc.) and the reasons why they were different. The term “foundational facts” will be strictly construed to prevent a party from offering a contrary opinion under the guise of impeachment.” (Fish at 146)
According to California Wine Association v. Commercial Union Fire Insurance Co. (1910) 159 C 49 at 56, sur-rebuttal evidence is limited to disproving matters in the opposing party’s rebuttal, rather than reiterating evidence already presented in the party’s case in chief.