The Deposition of the Adverse Expert Witness

By Darren O. Aitken


A party has the right to depose any expert designated by the opposing party. [CCP § 2034(i)]. In fact, any expert retained by the opposing side must be produced for deposition upon the service of proper notice. [CCP § 2034(h)]. The right to depose does not equate, however, with the obligation to depose, so the first consideration that counsel must make is whether to depose a particular expert prior to trial. The costs of such a deposition (including projected expert fees) must be balanced against the advantage of knowing an expert’s position prior to him or her taking the stand. This decision can be influenced by whether the expert in question has produced a detailed report (thereby reducing the threat of surprise), and by whether the expert is designated on an “unimportant” topic, or in an area where the parties are in substantial agreement. In some cases, it might not be worth the time or effort to depose a particular expert, but such a decision should be made with caution. Nothing prevents an expert from going beyond the subject matter of the report, or modifying (or even contradicting) the “preliminary” opinions contained the report. Therefore, in my opinion, deposing the opponent’s experts should be the general rule.


There is nothing in the Code of Civil Procedure (or case law for that matter), that indicates that one party has “priority” over the other in regard to the deposition of experts. Therefore, there is no authority for the oft heard argument that a plaintiff’s experts must be deposed before the defendant’s experts need be produced. In fact, in the expert witness declaration each attorney must attest to the “general substance” of the expert’s testimony, and affirm that the expert is ready to give a “meaningful” deposition in regard to his or her expected trial testimony. The requirement that one must declare one’s experts “ready” on the date the expert exchange is made effectively undercuts any contention that one side’s experts are required to be deposed first. Neither am I aware of any statutes or cases which hold that the first side to serve a deposition notice upon the other side has an absolute right of priority. In all cases, common sense, professional courtesy and a recognition of calendar conflicts should control.

To effectively depose an expert, an attorney needs access to that expert’s file and every document that he or she has relied upon to formulate his or her opinions. Furthermore, it is important to gather any and all information that could demonstrate to the jury that the expert is biased in favor of the party that has retained him or her. Unfortunately, Code of Civil Procedure section 2034 does not provide a mechanism for the production of the expert’s complete file and billing records. Section 2034(g) covers only “discoverable reports and writings”, which seems to indicate expert work product, and therefore compels the production of a much narrower category of documents than is needed. In fact, many experts do not prepare written reports at all. Therefore, a subpoena is required to get all the expert’s files on the matter. An alternate approach is to stipulate with opposing counsel that experts will voluntarily comply with a notice to produce and bring requested documents to the deposition (or to produce them on some mutually agreed upon date before the deposition) without the necessity of a subpoena.

My office typically requests the following documents:

  • Any and all reports, notes, memos, work sheets, and supporting data utilized in conjunction with the formulation of deponent’s opinion in this case and/or reviewed by him or her in investigating and reviewing this case;
  • Any and all writings or recordings which reflect any of deponent’s opinions in regard to this case;
  • Any and all correspondence in regard to this matter including, but not limited to, any correspondence to or from the hiring attorney and his or her firm;
  • Any and all business records which reflect time and effort on this matter, including but not limited to, invoices, hourly or daily charges, time sheets and ledgers;
  • If deponent has reviewed outside source material such as books or articles or other written materials which pertain to the subject matter of this litigation and relates to his or her investigation in this matter, then he or she is hereby requested to produce such material;
  • Any and all diagrams, sketches or demonstrative illustrations that the expert has created or relied upon in working on this matter, whether in draft or final form.
  • Any all video animations or visual recreations illustrating or pertaining to any of the expert’s opinions pertaining to this matter.
  • The deponent’s complete “file” in this matter.

This listing is general, and in particular cases we often ask for specific documents. This list is usually incorporated into a request for production attached to the deposition notice. As discussed above, however, some steps should be taken to ensure that there will be compliance with the notice.


When preparing one’s outline for the deposition of the opposing expert, it is helpful to keep in mind what one wants to accomplish. The objectives of a taking an expert’s deposition include:

  • Learning the opinions which the expert intends to express at trial, and getting as much information as possible on the bases for these opinions. In my opinion, the primary goal is to “pin the expert down” as much as possible. This prevents surprise at trial and allows one to craft one’s own presentation and cross of opposing witnesses.
  • Laying the groundwork for effective cross-examination at trial.
    • Getting the expert to commit to a specific position (and basis for that position) allows one to develop a strategy to “poke holes” in the expert’s conclusions at trial.
    • By learning what the expert believes is true, one can induce the expert to adopt as much of your client’s theory of the case as possible. These concessions can include both underlying facts and expert opinions.
    • Discovering ways to portray the expert as unqualified and/or a biased “hired gun” before the jury. The expert’s education, background and training need to be explored, with particular emphasis on the exact subject matter at hand. Bias questions include how much this particular witness has charged for his or her work on the matter, his or her history with the firm that has retained him or her, and the level of their involvement in legal matters in general.
    • Gathering all materials upon which the expert relied in forming those opinions, including both case-specific documents and general texts and treatises. These can be adopted by, commented upon or neutralized by one’s own experts (depending on the scenario), and one should look for inconsistencies between the expert’s opinions and the foundational material the expert has cited.
  • Discovering weaknesses in your clients’s case (at least as they are perceived by opposing counsel).
  • Assessing the demeanor and appearance of the expert.


With the above listed goals in mind, I have developed a simple checklist that I employ for the majority of the expert depositions that I take. It forms the backbone of my deposition outline, and to it I add case specific questions and hypotheticals.

Keep in mind the most important question at an expert deposition is “Why?”. Ironically, “Why?” is the worst question to ask an opposing expert (or any adverse witness, for that matter) at trial, but an effective deposition prevents trial counsel from having to take that dangerous road in front of the trier of fact.

  • Date expert first contacted on the case; when were materials received and when were opinions formed.
  • The number of hours spent on the matter; the number of hours that the expert anticipates to spend in the future.
  • Use the expert’s billing records to assess where the time was spent, and what was done by others in the office. Sometimes the testifying expert has had little contact with the file prior to deposition, and the bulk of the work was done by staff. On occasion, the staff member might have far more (or far less) expertise on the matters at issue than the “testifying” expert.
  • Inquire the nature of the future work to be done, and ask why it was not done prior to the deposition.
  • The expert’s fee, and how is it paid.
  • Also inquire the percentage of expert’s income from litigation matters.
  • Also determine the breadth of subjects upon which the expert renders “expert” testimony. Some experts are “jacks of all trades”, and can be attacked as such.
  • The expert’s credentials, especially in regard to the opinions rendered in this matter. Remember, an expert may have great credentials, but little training in this particular area. For example, an economist may have impeccable academic credentials, but little or no experience in conducting a tax audit.
  • Inquire into education, professional training and other life experiences that are relevant. Continuing education is important.
  • Memberships in professional organizations. What do those organizations do and what do they require for membership.
  • Seminars taught and papers written on the subject. Be sure to get copies of any articles in area written by this expert–they could be extraordinarily helpful as a potential source of impeachment.
  • Another source of impeachment material are advertising the expert has done and material on his or her website. In deposition, inquire whether the expert advertises his or her forensic services anywhere and whether he or she maintains a website.
  • The expert’s propensity to testify primarily for one side or the other (for example, plaintiff or defendant, police officer or citizen, etc.).
  • The expert’s history with the retaining attorney’s firm. Also, the history of the expert with the retaining lawyer, regardless of what firm he or she was employed with at the time, can provide useful information.
  • The expert’s assignment when hired, and any changes or modifications thereto. The expert designation provides a good starting point of this discussion. It is helpful to determine whether the description given is accurate and complete, or whether material mis-characterizations and omissions occurred.
  • What case-specific written materials were used, and for what purposes. For example, what depositions, written discovery, pleadings, exhibits, etc. were provided and studied? Also, was any attorney work product provided and studied?
  • What outside documents were used and for what purposes.
    • An opinion that contradicts the conclusion of a cited treatise can be very valuable at trial.
    • As per Evidence Code section 721(b), any treatise that is “recognized as reliable in the field” can be used to cross-examine, whether the expert used it or not. If you believe such a situation exists, try to get the expert to state the treatise is reliable at deposition, and then cross-examine with the contradictory statements at trial.
  • The subject areas upon which the expert intends to testify. The subject areas upon which the expert does not intend to testify. By limiting the subject matters of testimony, much time can be saved and surprises avoided (or limited) at trial. While it has been my experience that trial courts give ample “wiggle room” to experts to modify, or even contradict, their deposition testimony, they are much more likely to prevent an expert from opining on an area where they have previously stated that had no opinion.
  • Any written report (or notes) on this matter, or other documentation of thoughts and conclusions. When they exist, written reports typically reflect the expert’s chief opinions and should be examined closely. If such a report exists, it is important that you ask the witness to explicitly confirm his agreement with the findings and conclusions contained in the report. (This is an additional method of “pinning the witness down”.)
  • Any persons interviewed or consulted on this matter.
  • The opinions the experts has reached, and the bases for these opinions.
  • This is the key “What?” question.
  • For each particular case, the attorney should prepare a list of the key topics in this expert’s area of expertise.
  • Be as slow and laborious as necessary.
  • Have the expert state which evidence supports which theory. In other words, “Why?”. If appropriate, determine if changed facts changes the opinion.
  • Elicit information in order to allow you to assess the validity of the support for each opinion. Remember, “garbage in, garbage out”.
  • Clarify the factual assumptions upon which the expert is relying. By “assumption”, I mean conclusions drawn from sources other than physical evidence and testing. For example, in a vehicle collision case, the experts’ opinion of the speed of a particular vehicle might be based solely on the statement of a party or witness. This is important to know if there is physical evidence or witness testimony that contradicts that assumption, and allows the deposing attorney to have the expert clarify that if the assumed testimony is shown to be false or inaccurate, his opinion is no longer valid.
  • What areas of agreement, both factual and opinion, between opposing expert and your side’s theory of the case. For example, a series of questions can be posed confirming that the expert agrees with certain core facts upon which your case also relies. For example, “You agree, Ms. Smith, that my client’s business’s annual profits were no less than $100,000 per year over the ten year period preceding the fire?”. By confirming this sort of facts, one both bolsters one’s own case (and experts) and prevents the expert from taking a contrary position at trial.
  • Any experiments or recreations that were done, and for what purposes, and whether any planned in the future. Recreations and experiments being planned following the deposition are a real danger area and, in my opinion, justify a second deposition or blocking the post-deposition evidence from trial.
  • Any exhibits or other demonstrative evidence prepared, or is being planned in the future for trial. If something elaborate is being planned but not yet prepared, such as a animated recreation, I would object on the record and preserve the right to examine the video, re-depose the witness on its contents and to lodge appropriate objections regarding admissibility at trial.
  • Examine all the contents of the produced file to determine whether further inquiry is warranted. Often, copied articles, billing, phone messages, handwritten notes and/or intra-office memos can clarify, limit or undermine the expert’s “scripted” answers given in response to direct questioning. Insights and impeachment material may be gleaned from analyzing what was and was not reviewed prior to the deposition.
  • At the conclusion of the deposition, always inquire whether there are any other major areas of testimony that the expert has prepared for trial that has yet to be discussed. Also, inquire whether the experts has “any more opinions” relating to the litigation at hand. While this question typically elicits an objection and a response that “it depends on the questions asked”, I do believe they serve to limit somewhat the expert’s ability to expand his or her testimony by the time of trial. In response to any such objection or vague response, make it clear on the record that the deposition is your only opportunity to learn this person’s opinions, and that the purpose of the deposition is to prevent surprise at trial.

5. MY FAVORITE QUESTIONS (The Shorthand Way Of Looking At It)

About ninety percent of the above section’s discussion is covered by using the following list of simple questions as many times as necessary until the expert runs out of things to say.

  • What was your assignment in this case?
  • What are the areas about which you expect to testify?
  • What opinion(s) do you hold in regard to that topic?
  • Why do you hold that opinion?
  • What material in your file supports that opinion?
  • Did you rely on anything outside of your file as a basis for that opinion?
  • What aspect of your education [or background or training] qualifies you to offer that opinion?
  • Have you prepared (or will you prepare) any exhibits pertaining to this opinion?
  • What is the significance of this document from your file?
  • Is there any additional work that you intend to do before trial on this topic?
  • Are there other areas pertaining to this matter that we haven’t discussed that you have prepared opinions on?

These questions need to be repeated for each topic, and for each opinion within a topic, as needed. At the risk of repeating myself, the goal is to methodically obtain a detailed list of each and every opinion, and each and every basis for that opinion.


The focus of the expert deposition revolves around the “what” and the “why”. In other words, “What do you believe?” and “Why do you believe it?”. Keeping this focus in mind allows one to question the opposing expert in an organized and methodical manner, and effectively “pins down” the expert so that his or her ability to present different opinions at trial is compromised.

Contact Aitken * Aitken * Cohn today to learn more.