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Retained and Non-retained Expert Witnesses – Part III: Supplemental Expert Designations

Kat S. Hatziavramidis, Esq.

July 14, 2015



The California Code of Civil Procedure (C.C.P.) provides attorneys with guidelines that establish when and how to disclose and designate expert witnesses. This article addresses proper versus improper supplemental expert witness designations and provides assistance to practitioners who wish to make a supplemental designation.


According to a California legal analyst, practitioners frequently make the mistake of misunderstanding the nature and purpose of the supplemental expert designation provisions that the C.C.P. lays out.

Brian Chase, “Don't Designate an 'Inexpert' Expert,” Advocate, Jul. 2011. C.C.P § 2034.280 provides that parties who have exchanged the information that the C.C.P. requires to comply with the initial expert disclosure measures have the option of submitting a supplemental list of expert witnesses within 20 days, but only under certain circumstances.

As one attorney has explained, however, attorneys often mistakenly attempt to utilize the supplemental procedure, with the two most common mistakes being improperly “attempting to use the Supplemental a vehicle for further initial designation (including substituting initially-designated experts); and (2) supplementally designating an expert witness whose area of opinion is not responsive to an area of expertise initially designated by an adverse party.” Chase, id.

The Supreme Court of California has made it clear that its intent in interpreting the C.C.P. is to construe the restrictions of C.C.P. § 2034.280 narrowly. See, e.g., Basham v. Babcock, 44 Cal. App. 4th 1717, 1723 (1996) (holding that the limitations set forth in the C.C.P. are mandatory and are to be narrowly construed, given the importance of early and simultaneous exchange of expert witness disclosures).

The Court, in Basham v. Babcock, dealt with a party that had originally designated one medical expert to provide an opinion regarding causation, but that later used the C.C.P. to supplement the initial designation by disclosing a new medical expert to give an opinion on the same matter. See id.

However, the Basham Court held that the new opinion should be excluded from the trial testimony because “the plain language of § 2034.280(a)...holds that a party may only use a supplemental expert designation if the party supplementing the expert witness list has not previously retained an expert to testify on that subject." Id. at 1724.

The Basham opinion should put attorneys on notice, making them take care when they choose who they wish to designate as an expert witness, both initially and in any supplemental procedures.

Attorneys should be careful to make sure that the person they originally disclose to adverse parties as their expert on a particular matter is the person whom they feel can most strongly support their case at trial.

Both the C.C.P. and the courts clearly frown on attorneys who choose and designate one expert and then find someone whom they feel is more qualified and attempt to “switch” experts, by using the supplemental designations.

Accordingly, practitioners should thoroughly vet their experts early, thereby making it unnecessary to go back later and attempt to change experts after the initial discovery period that provides for the disclosure and designation of initial experts.

The second most common mistake that attorneys make in dealing with supplemental designations concerns is attempting to designate experts to provide opinions on subjects that are not covered by an “expert designated by an adverse party to the exchange.” C.C.P. § 2034.280(a); See Chase, supra.

In other words, if an expert could have been designated in the initial exchange of expert information, they should have been.

Attorneys who attempt to supplementally designate an expert and thereby delay discovery about that expert face hostile courts and a set of rules that does not permit such an abuse of the C.C.P. See id.

To wit, “ supplemental designation...cannot be employed to add new experts that could have been designated in the initial exchange of information, but may have been overlooked by the designating party at the time.

Unless the adverse party had designated an expert in that specific area, such a nonresponsive supplemental designation is violative of § 2034.280, will likely result in exclusion of such improperly designated expert(s).” Id.


Both the C.C.P. and the California courts have made it clear that the purpose and nature of the supplemental expert designations are quite narrow and that, furthermore, any deviations from or violations of such provisions will result in inappropriately supplemented experts being excluded from giving any opinions whatsoever.

Attorneys who are unsure of what to do may do well to follow the advice of one commentator: “When in doubt, the most advisable course of action is therefore to move as timely as the need is perceived, for leave to augment your initial designation, pursuant to C.C.P., § 2034.620.” Id. In so doing, California practitioners can avoid many headaches and will have the best chances of getting the opinions they need included at trial.

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