Expert Depositions: Taking Apart the Opinion, Protecting Your Own Expert, and Building the Daubert Record

Summary. An expert deposition is where a Daubert motion is won or lost, and where the trial cross-examination is either built or thrown away. This article explains the rules that govern expert discovery in federal court: the Rule 26(a)(2) report and summary requirements, the sequencing and rebuttal windows, the 2010 work product protection for drafts and attorney-expert communications and its three exceptions, consulting-expert immunity, who pays the expert's fee, supplementation, and the exclusion remedy of Rule 37(c)(1). It then works through the evidence rules the deposition is built around, including the December 2023 amendment to Rule 702, and the cases that define reliability, from Daubert, Joiner, and Kumho Tire to Sardis, Paoli, and Elcock, with the patent damages line from Uniloc through Exmark as the running example of the ipse dixit problem. The second half is technique: the goals of the taking lawyer, the funnel structure, bias and prior testimony, the learned-treatise setup, hypotheticals, closing the doors, and the mistakes that waste the day; then the defending lawyer's job, from preparation sessions and privilege to objections, instructions, errata, and supplementation. Reliance material subpoenas, fee disputes, remote depositions, dual-hat and formerly consulting experts, foreign experts, and the use of the transcript at trial and on summary judgment round it out, with worked examples from a patent royalty deposition and a copyright software expert defense.

The damages expert's report runs 140 pages, has 19 exhibits, and concludes that a reasonable royalty for the accused Wi-Fi chipset feature is $212 million. Buried on page 61 is a sentence that will decide the case: "I have been instructed by counsel to assume that the '417 patent is essential to the 802.11ac standard." Nobody in the room will mention that sentence unless you do. If you spend the deposition arguing with the economist about discount rates, you will leave with seven hours of transcript and nothing to file.

An expert deposition is not a fact deposition with a smarter witness. The witness has already written down everything she intends to say, the rules protect most of what went into writing it, the other side is paying her by the hour to sit there, and the only questions that matter are the ones that map onto the four elements of Rule 702. That is the whole game: lock the opinions, find the assumptions, test the method against the field, and leave with the admissions a judge needs to exclude the testimony or a jury needs to discount it.

The short answer

In federal court a retained expert may be deposed only after serving a written report (Fed. R. Civ. P. 26(b)(4)(A)), the deposition is presumptively one day of seven hours (Fed. R. Civ. P. 30(d)(1)), and the party taking it pays the expert a reasonable fee for the time (Fed. R. Civ. P. 26(b)(4)(E)). Draft reports and most attorney-expert communications are work product under Rule 26(b)(4)(B) and (C), with three exceptions you can always ask about: what the expert is paid, the facts or data counsel supplied that the expert considered, and the assumptions counsel supplied that the expert relied on. Everything else the expert considered, from whatever source, is fair game and should already have been disclosed with the report.

The deposition exists to serve two later events. The first is a motion under Fed. R. Evid. 702, which since December 1, 2023 requires the proponent to show that it is "more likely than not" that the opinion rests on sufficient facts, reliable methods, and a reliable application of those methods. The second is trial, where the transcript becomes the script for impeachment and the boundary of what the expert may say. A taking lawyer who understands both events asks short, closed questions organized around the elements of Rule 702, obtains the expert's agreement that the report is complete, and extracts the concessions about assumptions and alternatives that a brief can quote. A defending lawyer prepares the expert to answer from the report, to recognize the three privilege exceptions, to resist the hypothetical that quietly swaps out the facts, and to say "that is outside what I was asked to do" without sounding evasive.

For the disclosure machinery and the Daubert motion itself, this article leans on two existing resources, Expert Witnesses After the 2023 Amendment to Rule 702: Daubert, Disclosure, and Cross-Examination and the Expert Witness Toolkit. The focus here is the deposition itself. The procedural, step-by-step version is Taking and Defending an Expert Deposition: A Practical Guide; the working documents are in the Expert Deposition Toolkit and the Expert Deposition Preparation Checklist.

The rules that govern expert discovery

Expert discovery in federal court is almost entirely a creature of Fed. R. Civ. P. 26, supplemented by the deposition mechanics of Rule 30 and the exclusion remedy of Rule 37(c)(1). The table is the map; the sections that follow explain how each piece actually works.

Reports and summaries: who must write what

The report under Fed. R. Civ. P. 26(a)(2)(B) must contain six things: a complete statement of all opinions and the basis and reasons for them; the facts or data considered in forming them; any exhibits that will be used to summarize or support them; the witness's qualifications, including publications from the prior ten years; a list of all other cases in which the witness testified as an expert at trial or by deposition during the prior four years; and a statement of the compensation to be paid. The Seventh Circuit's explanation in Salgado v. General Motors Corp., 150 F.3d 735 (7th Cir. 1998), is still the best one-sentence statement of purpose: the report must be complete enough that opposing counsel is not forced to depose the expert to avoid an ambush at trial. The report does not, however, have to attach every working note; the First Circuit said so in Gillespie v. Sears, Roebuck & Co., 386 F.3d 21 (1st Cir. 2004), and that is why a subpoena for the file is often still necessary.

Non-retained experts are different. A treating physician who will testify that the patient's wrist injury was caused by the fall, or a company's chief architect who will explain why the accused module could not have been copied from the plaintiff's code, is a witness who formed opinions in the course of doing a job rather than in the course of being hired for the lawsuit. The 2010 amendments added Rule 26(a)(2)(C) to require a short summary disclosure for these witnesses: the subject matter and a summary of the facts and opinions. The Advisory Committee's note to the 2010 amendments explains that the summary is meant to be considerably less extensive than a report, and courts police the line in both directions. An employee who strays from what she learned on the job into opinions she formed by reviewing litigation materials becomes, as to those opinions, a witness who needed a full report. Wright & Miller discuss the treating-physician boundary at 8A Federal Practice and Procedure § 2033 (3d ed.).

Sequence and the 30-day rebuttal window

Absent a stipulation or court order, Fed. R. Civ. P. 26(a)(2)(D) sets the default: expert disclosures at least 90 days before trial, and rebuttal disclosures, limited to contradicting or rebutting evidence on the same subject matter identified by another party, within 30 days after the other party's disclosure. In practice the scheduling order under Fed. R. Civ. P. 16 replaces the defaults with a staggered schedule: opening reports from the party with the burden (infringement, damages, likelihood of confusion), rebuttal reports from the other side roughly 30 days later, sometimes reply reports, and then a window for expert depositions before the Daubert and summary judgment deadlines.

Two consequences follow. First, you cannot depose an expert on a report that has not been served, so a rebuttal expert is deposed after the rebuttal report and the opening expert is often deposed only after seeing what the rebuttal said. Second, a "rebuttal" report that introduces new affirmative opinions is vulnerable to a motion to strike, because the rule limits rebuttal to the same subject matter. The deposition is where you establish, in the expert's own words, which opinions are responsive and which are new.

Rule 26(b)(4)(A): deposition only after the report

The rule that a report-required expert may be deposed only after the report is served sounds like a technicality, but it has a practical bite. The taking lawyer gets a fixed target. The defending lawyer gets a shield: anything not in the report is, by definition, not an opinion the expert has disclosed, and the witness can decline to speculate beyond it. The 1993 Advisory Committee note, which introduced the report requirement and the routine right to depose, is discussed in Wright & Miller § 2031.1, and the note's premise bears repeating: the report was supposed to make many expert depositions unnecessary or at least shorter. That has not happened, and no litigator should plan as though it will.

Rule 26(b)(4)(B) and (C): drafts, communications, and the three exceptions

Before December 1, 2010, most circuits treated everything a lawyer handed a testifying expert as discoverable, the lawyer's own strategy memos included, on the theory that the expert had "considered" it. The Sixth Circuit called it a bright-line rule in Regional Airport Authority of Louisville v. LFG, LLC, 460 F.3d 697 (6th Cir. 2006), and the Federal Circuit applied the same approach in In re Pioneer Hi-Bred International, Inc., 238 F.3d 1370 (Fed. Cir. 2001). The behavior it produced was predictable and expensive. Lawyers stopped writing to their experts, hired a second "shadow" consultant to do the real thinking, and then spent deposition hours on the twelfth draft of a report instead of on the opinion in it.

The 2010 amendments changed that with two provisions. Fed. R. Civ. P. 26(b)(4)(B) extends work product protection (the doctrine that grew out of Hickman v. Taylor, 329 U.S. 495 (1947) and now lives in Rule 26(b)(3), shielding materials prepared in anticipation of litigation) to drafts of any report or disclosure required by Rule 26(a)(2), "regardless of the form in which the draft is recorded." Rule 26(b)(4)(C) protects communications between the party's attorney and an expert required to give a report, again regardless of form, except to the extent the communications:

1. relate to compensation for the expert's study or testimony;
2. identify facts or data that the party's attorney provided and that the expert considered in forming the opinions to be expressed; or
3. identify assumptions that the party's attorney provided and that the expert relied on in forming the opinions to be expressed.

Read the verbs closely, because the deposition turns on them. Facts or data are discoverable if the expert considered them, which is broad: the Advisory Committee's note to the 2010 amendments says "facts or data" should be "interpreted broadly to require disclosure of any material considered by the expert, from whatever source, that contains factual ingredients," and courts read "considered" to include anything the expert "generates, reviews, reflects upon, reads, and/or uses" in forming the opinions, even material the expert ultimately rejected, as in Synthes Spine Co. v. Walden, 232 F.R.D. 460 (E.D. Pa. 2005). Assumptions are discoverable only if the expert relied on them, which is narrower. So the productive questions are "What did counsel send you?" and "What were you told to assume?" The unproductive one, now, is "What did counsel say about your second draft?"

Three refinements matter in practice. First, the protection is work product protection, so in theory it yields to a showing of substantial need under Rule 26(b)(3)(A)(ii); the Committee Note predicts such showings will be rare, and they are. Second, Rule 26(b)(4)(C) covers only experts who must write a report. Communications between counsel and a non-retained Rule 26(a)(2)(C) witness, such as a treating physician or the client's own engineer, are not protected by it, although drafts of the (C) disclosure are; see PacifiCorp v. Northwest Pipeline GP, 879 F. Supp. 2d 1171 (D. Or. 2012). Third, parties can change the default by agreement under Fed. R. Civ. P. 29, and many do: a short expert stipulation that drafts, notes, and attorney communications are off limits for both sides saves money and removes a category of deposition fights. Some state courts have no equivalent of the 2010 protections, which is why multistate litigators write the stipulation into the protective order.

What the 2010 amendments did not protect

When the Republic of Ecuador sought the files of Chevron's experts through 28 U.S.C. § 1782 proceedings around the country, Chevron argued that the 2010 amendments, read with Rule 26(b)(3), created a general work product shield for everything a testifying expert touched. Three circuits rejected the argument: Republic of Ecuador v. Mackay, 742 F.3d 860 (9th Cir. 2014), Republic of Ecuador v. Bjorkman, 735 F.3d 1179 (10th Cir. 2013), and Republic of Ecuador v. Hinchee, 741 F.3d 1185 (11th Cir. 2013). The protections are specific, not general. Drafts and attorney-expert communications are covered; the expert's own development of the opinions is not.

That leaves a great deal open at the deposition: the expert's notes and working papers, testing and the notes of testing, analyses the expert ran and abandoned, communications with anyone other than the retaining lawyer (the client's engineers, a co-expert, the expert's own staff), and every document the expert considered. The Seventh Circuit's decision in Fidelity National Title Insurance Co. v. Intercounty National Title Insurance Co., 412 F.3d 745 (7th Cir. 2005) shows the stakes. A forensic accountant's team discarded interview notes it thought irrelevant to the opinion. The court held that a testifying expert must disclose, and therefore retain, the materials given to him to review even if he does not rely on them, and that a document-retention policy cannot trump Rule 26(a)(2)(B). (It also held that excluding the expert was too harsh a sanction on those facts and ordered a new trial, a point the defending lawyer should remember when the other side asks for the death penalty.)

Rule 26(b)(4)(D): consulting experts, and the consultant who becomes a witness

A consulting expert is one retained or specially employed in anticipation of litigation who is not expected to testify. Under Fed. R. Civ. P. 26(b)(4)(D), the other side ordinarily may not discover the facts known or opinions held by that expert, by interrogatory or deposition, except under Fed. R. Civ. P. 35(b) (reports of examining physicians) or on a showing of exceptional circumstances that make it impracticable to obtain the same information by other means. The classic exceptional circumstance is destructive testing: the consultant examined the only failed part, and the examination consumed it. The Tenth Circuit in Ager v. Jane C. Stormont Hospital & Training School for Nurses, 622 F.2d 496 (10th Cir. 1980) extended the protection to the consultant's identity, though not every court goes that far. Wright & Miller collect the cases at 8A Federal Practice and Procedure § 2032.

The trouble starts when a consultant is promoted to testifier. Designation ends the consulting protection for everything that bears on the testimony, and courts resolve doubts against the party that blurred the roles. In Yeda Research & Development Co. v. Abbott GmbH & Co. KG, 292 F.R.D. 97 (D.D.C. 2013), a scientist had observed the opponent's experiments as a consultant years earlier and was later designated to testify on the same subject. The court held that the designation waived work product protection over the consulting work, observing that even a highly educated expert "cannot be expected to draw a mental line in the sand" between what he learned in each role. The lesson for the retaining side is structural: keep the consultant and the testifier in different people, or assume the consultant's whole file will be produced. The lesson for the taking side is to ask, early, "When were you first contacted about this matter, and what did you do before you were asked to write a report?"

Rule 26(b)(4)(E): who pays for the deposition

Unless manifest injustice would result, Fed. R. Civ. P. 26(b)(4)(E)(i) requires the party seeking discovery to pay the expert a reasonable fee for time spent responding. Disputes cluster around four questions: whether the hourly rate is reasonable (courts look at the expert's field and credentials, prevailing rates for comparable experts, the complexity of the subject, and what the expert charges the side that hired her); whether preparation time is compensable (district courts split, and many split the difference by allowing a reasonable multiple of deposition time); whether travel counts; and whether the deposing party pays for the expert's review of the transcript. Agree on all four in writing before the deposition notice goes out.

Keep this fee separate from fee-shifting at the end of the case. Absent a statute or contract that says otherwise, an expert's charges are not taxable costs beyond the ordinary witness fee and allowances of 28 U.S.C. § 1821; Crawford Fitting Co. v. J.T. Gibbons, Inc., 482 U.S. 437 (1987) read 28 U.S.C. § 1920 that way. A client who assumes the loser pays for the experts is usually wrong, and should hear that before retaining three of them.

Supplementation under Rule 26(e) and exclusion under Rule 37(c)(1)

For a report-required expert, Fed. R. Civ. P. 26(e)(2) extends the duty to supplement to both the report and the information given at the deposition, and the supplement is due by the time of the Rule 26(a)(3) pretrial disclosures. Supplementation means correcting and completing, not improving. The court in Keener v. United States, 181 F.R.D. 639 (D. Mont. 1998) limited it to "correcting inaccuracies, or filling the interstices of an incomplete report based on information that was not available at the time of the initial disclosure," and Akeva L.L.C. v. Mizuno Corp., 212 F.R.D. 306 (M.D.N.C. 2002) refused to treat bolstering as supplementation because that would amount to "unlimited expert opinion preparation." Beller ex rel. Beller v. United States, 221 F.R.D. 689 (D.N.M. 2003) put it in a phrase litigators repeat: no deeper, broader, or stronger opinions built on information the expert already had.

The enforcement mechanism is Fed. R. Civ. P. 37(c)(1): information or a witness not disclosed as Rule 26(a) or (e) requires may not be used on a motion, at a hearing, or at trial unless the failure was substantially justified or harmless. The Ninth Circuit calls the rule self-executing and puts the burden of proving harmlessness on the party that failed to disclose, Yeti by Molly, Ltd. v. Deckers Outdoor Corp., 259 F.3d 1101 (9th Cir. 2001). The Fourth Circuit weighs surprise, the ability to cure it, disruption of trial, the importance of the evidence, and the explanation for the failure, Southern States Rack & Fixture, Inc. v. Sherwin-Williams Co., 318 F.3d 592 (4th Cir. 2003). The Third Circuit's older Meyers v. Pennypack Woods Home Ownership Ass'n, 559 F.2d 894 (3d Cir. 1977) adds that excluding critical evidence is an extreme sanction. The results can be dramatic. In Rembrandt Vision Technologies, L.P. v. Johnson & Johnson Vision Care, Inc., 725 F.3d 1377 (Fed. Cir. 2013), the patentee's expert described one hardness-testing method in his report and a different one on the stand; the district court struck his testimony and the Federal Circuit affirmed. In MLC Intellectual Property, LLC v. Micron Technology, Inc., 10 F.4th 1358 (Fed. Cir. 2021), the court affirmed both a Daubert exclusion of a royalty opinion that failed to apportion and the striking of a royalty-rate theory whose factual basis had not been disclosed in discovery.

The deposition is where you lay the foundation for that motion. Three questions do most of the work: "Does your report contain every opinion you intend to offer at trial?" "Have you formed any opinion since signing it?" and "Do you plan to do any further work?" If new opinions surface later, the transcript proves they are new.

Rule 30: seven hours, objections, and instructions

Fed. R. Civ. P. 30(d)(1) limits a deposition to one day of seven hours, counting only time on the record, and requires the court to allow more time if needed to examine the witness fairly. Experts who cover several patents, several reports, or both liability and damages routinely get more, but the better practice is to negotiate time per report in the scheduling order rather than fight about it at hour six. Rule 30(c)(2) requires objections to be stated "concisely in a nonargumentative and nonsuggestive manner" and allows an instruction not to answer only to preserve a privilege, to enforce a court-ordered limitation, or to present a Rule 30(d)(3) motion to terminate or limit a deposition conducted in bad faith or to annoy, embarrass, or oppress. The Seventh Circuit's opinion in Redwood v. Dobson, 476 F.3d 462 (7th Cir. 2007) is the standard citation for what happens when lawyers ignore those limits. And because the rules on conferring with the witness during the deposition vary, check whether your court follows Hall v. Clifton Precision, 150 F.R.D. 525 (E.D. Pa. 1993), which barred lawyer-witness conferences during the deposition except to decide whether to assert a privilege and treated break-time conferences as a proper subject of questioning. Many courts are more permissive; few are more restrictive.

The evidence rules the deposition is really about

Every good question at an expert deposition is aimed at an evidence rule the judge will apply later. Lawyers who prepare from the procedural rules alone take long depositions that never connect to the motion.

Rule 702 after December 1, 2023

As amended, Fed. R. Evid. 702 allows a qualified expert to testify "if the proponent demonstrates to the court that it is more likely than not that" (a) the expert's specialized knowledge will help the trier of fact; (b) the testimony is based on sufficient facts or data; (c) the testimony is the product of reliable principles and methods; and (d) the expert's opinion reflects a reliable application of the principles and methods to the facts of the case. The preponderance standard was always the law under Fed. R. Evid. 104(a) and Bourjaily v. United States, 483 U.S. 171 (1987). What changed is that it is now in the text, and the Advisory Committee's note explains why in unusually pointed language: "many courts have held that the critical questions of the sufficiency of an expert's basis, and the application of the expert's methodology, are questions of weight and not admissibility. These rulings are an incorrect application of Rules 702 and 104(a)." The rewritten subsection (d) is aimed at overstatement; the note says each opinion "must stay within the bounds of what can be concluded from a reliable application of the expert's basis and methodology."

For the deposition, that means two things. The taking lawyer should build the record element by element and opinion by opinion, because the proponent now must carry each element for each opinion, and a concession that defeats one element defeats the opinion. The defending lawyer should make sure the expert can articulate, in plain words, the method, why it is reliable, and how it was applied, because "I used my judgment" will not carry a preponderance burden. For the history, the trilogy, and the motion practice, see Expert Witnesses After the 2023 Amendment to Rule 702 and the Expert Disclosure and Daubert Challenge Checklist.

Rules 703 and 705: what the expert may rely on, and what she can skip at trial

Under Fed. R. Evid. 703, an expert may rely on facts or data that experts in the field would reasonably rely on, even if they are inadmissible, but the proponent may disclose inadmissible bases to the jury only if their value in helping the jury evaluate the opinion substantially outweighs their prejudicial effect. Rule 703 is not a hearsay conduit. In Mike's Train House, Inc. v. Lionel, L.L.C., 472 F.3d 398 (6th Cir. 2006), the Sixth Circuit held both that a novel method for detecting copying in design drawings was unreliable and that the expert's recitation of another person's conclusions was improper under Rule 703. Judge Posner's version of the point in Dura Automotive Systems of Indiana, Inc. v. CTS Corp., 285 F.3d 609 (7th Cir. 2002) is the one to quote: an expert may rely on assistants and on other experts' work, but a scientist "is not permitted to be the mouthpiece of a scientist in a different specialty." At the deposition, that translates into "Who ran these numbers?" and "Could you have done that analysis yourself?"

Fed. R. Evid. 705 lets an expert state an opinion at trial without first testifying to the underlying facts, unless the court orders otherwise, and leaves it to cross-examination to bring them out. That is a gift to the proponent and a warning to the opponent: if you have not extracted the foundation at the deposition, you will be doing it live, in front of the jury, with a witness who has had months to rehearse.

Rule 803(18): the learned-treatise setup

Fed. R. Evid. 803(18) admits statements in a treatise, periodical, or pamphlet if they are called to the expert's attention on cross-examination (or relied on in direct) and the publication is established as a reliable authority by the expert's admission, by another expert, or by judicial notice. If admitted, the passage is read into evidence but not received as an exhibit. The foundation is the part lawyers forget. The deposition is the cheap place to get it: "Do you consider the Reference Manual on Scientific Evidence authoritative on regression analysis? Is the IEEE standard the one engineers in your field follow?" An expert who agrees at deposition has made the treatise usable at trial; an expert who refuses has told you to line up your own expert to lay the foundation. The rule is not limited to paper; the Second Circuit accepted a videotape as a learned treatise in Costantino v. Herzog, 203 F.3d 164 (2d Cir. 2000).

Prior statements: Rules 613 and 801

An expert's earlier report, article, or testimony that contradicts today's opinion is impeachment under Fed. R. Evid. 613, which admits extrinsic proof of the statement only if the witness gets a chance to explain or deny it. A deposition answer that the expert contradicts at trial is more than impeachment: under Fed. R. Evid. 801(d)(1)(A), a prior inconsistent statement given under penalty of perjury at a deposition is not hearsay and can be used for its truth. That is one more reason to ask the clean, closed question at the deposition and to get a clean, closed answer.

The leading cases, explained

The trilogy and what each case means in the deposition room

Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579 (1993) made the trial judge a gatekeeper and offered a non-exclusive list of reliability considerations: whether the theory can be and has been tested, whether it has been peer reviewed and published, its known or potential error rate, the existence of standards controlling its operation, and its general acceptance. Each factor is a deposition chapter. General Electric Co. v. Joiner, 522 U.S. 136 (1997) held that exclusion rulings are reviewed for abuse of discretion and supplied the sentence every Daubert brief quotes: nothing requires a court "to admit opinion evidence that is connected to existing data only by the ipse dixit of the expert," because a court "may conclude that there is simply too great an analytical gap between the data and the opinion proffered." Kumho Tire Co. v. Carmichael, 526 U.S. 137 (1999) extended gatekeeping to every kind of expert, technical and experience-based included, and asked whether the expert "employs in the courtroom the same level of intellectual rigor that characterizes the practice of an expert in the relevant field." That last sentence generates the single most useful question at an expert deposition: "If a client had hired you to answer this question outside of litigation, what would you have done that you did not do here?" Finally, Weisgram v. Marley Co., 528 U.S. 440 (2000) held that when an appellate court finds expert testimony inadmissible and the rest of the evidence insufficient, it may direct judgment for the other side. Parties get no second try at expert proof, which is why the deposition record matters on appeal too.

Paoli and the "any step" principle

The Third Circuit's decision in In re Paoli Railroad Yard PCB Litigation, 35 F.3d 717 (3d Cir. 1994) held that "any step that renders the analysis unreliable under the Daubert factors renders the expert's testimony inadmissible," whether the flaw changes a reliable method or merely misapplies it. The Second Circuit adopted the formulation in Amorgianos v. National Railroad Passenger Corp., 303 F.3d 256 (2d Cir. 2002), and the 2023 amendment to subsection (d) codifies its spirit. Paoli also said something about depositions that defending lawyers should cite when the other side tries to file a Daubert motion without letting them depose its own expert: because the in limine findings can decide the case, "it is important that each side have an opportunity to depose the other side's experts." The deposition method that follows from Paoli is to walk the analysis one step at a time and get the expert to agree on what each step is before testing any of them. Consistency matters too; in In re Zoloft (Sertraline Hydrochloride) Products Liability Litigation, 858 F.3d 787 (3d Cir. 2017), the court affirmed exclusion of an expert who did not apply his own chosen methodology consistently.

Elcock: unreproducible methods and castles made of sand

Elcock v. Kmart Corp., 233 F.3d 734 (3d Cir. 2000) is two lessons in one opinion. The plaintiff's vocational rehabilitation expert used a method the court found subjective and unreproducible, and the Third Circuit held that a Daubert hearing should have been held before he testified (while upholding his qualifications despite his lack of formal training in the field). The economist's lost-earnings model rested on assumptions about the plaintiff's disability and earning capacity that had no foundation in the record; an opinion built on such assumptions, the court said, is a castle made of sand. The economic damages award fell with both of them. The Second Circuit's Boucher v. U.S. Suzuki Motor Corp., 73 F.3d 18 (2d Cir. 1996) reached the same place on an earnings assumption contradicted by the evidence. At the deposition, the reproducibility question is "If I gave your inputs to another qualified expert, would she reach your number? How do you know?" and the foundation question is "Where in the record does this assumption come from?"

Sardis and Nease: the Fourth Circuit's gatekeeping cases

In Sardis v. Overhead Door Corp., 10 F.4th 268 (4th Cir. 2021), the district court admitted two plaintiff's experts after treating the defendant's reliability objections as going to weight, and the jury returned a $4.84 million verdict. The Fourth Circuit held that the court had abdicated its gatekeeping role, that both experts' testimony was inadmissible, and, following Weisgram, directed entry of judgment for the defendant. Two details make the case a deposition lesson. The court relied on the Advisory Committee's then-pending proposal to amend Rule 702, two years before it took effect. And one expert, asked about the testing standards a manufacturer should have followed, pointed the jury to "Google" for standards he could not identify. The question that produces that answer is simple: "Name the standard. Which edition? Which section? Show me where it says that." Nease v. Ford Motor Co., 848 F.3d 219 (4th Cir. 2017) is the companion: an engineer's theory of how a speed-control cable could bind was a hypothesis he never tested, and the court held that a hypothesis is not knowledge under Rule 702.

Experience-based experts and expert intuition

Experience can qualify an expert and supply a method, but only if the expert explains how. The en banc Eleventh Circuit in United States v. Frazier, 387 F.3d 1244 (11th Cir. 2004), echoing the 2000 Advisory Committee note, required an experience-based witness to explain how the experience leads to the conclusion, why it is a sufficient basis, and how it was reliably applied to the facts. Judge Easterbrook was blunter in Zenith Electronics Corp. v. WH-TV Broadcasting Corp., 395 F.3d 416 (7th Cir. 2005): an expert who relied on "expert intuition" and a party's internal projections, which "represent hopes rather than the results of scientific analysis," did not satisfy Rule 702. When an expert answers "based on my thirty years of experience," the follow-up is "Walk me through how your experience produced 7 percent rather than 5 or 9."

The patent damages line: the ipse dixit problem in its purest form

Patent damages under 35 U.S.C. § 284 must be "adequate to compensate for the infringement, but in no event less than a reasonable royalty," and the reasonable royalty is usually modeled as a hypothetical negotiation using the fifteen factors of Georgia-Pacific Corp. v. United States Plywood Corp., 318 F. Supp. 1116 (S.D.N.Y. 1970). The requirement that damages be apportioned to the patented feature goes back to Garretson v. Clark, 111 U.S. 120 (1884). Over the last fifteen years the Federal Circuit has policed royalty experts more closely than any other category, and nearly every holding converts into a deposition question.

The common thread is the ipse dixit problem. A royalty expert's report recites the fifteen factors, describes the parties, and then announces a number. The deposition's job is to find the step where judgment replaced method, and to get the expert to say so. The best questions are quantitative and closed: which factor, which direction, how much, based on what document. For deeper treatment of the doctrine, see Patent Damages: Reasonable Royalties, Lost Profits, Apportionment, and Enhancement and the Patent Damages Toolkit; the same discipline applies to unjust-enrichment and royalty experts in trade secret cases, covered in Trade Secret Damages and Remedies.

How courts actually apply it: the weight-versus-admissibility divide

Before the amendment, the circuits sorted into two habits, and you will still see both in briefs. One habit treated the inputs and application of an expert's analysis as jury questions. The Seventh Circuit wrote in Smith v. Ford Motor Co., 215 F.3d 713 (7th Cir. 2000) that "the soundness of the factual underpinnings of the expert's analysis and the correctness of the expert's conclusions based on that analysis are factual matters to be determined by the trier of fact." The Ninth Circuit reversed an exclusion in City of Pomona v. SQM North America Corp., 750 F.3d 1036 (9th Cir. 2014) with the line that "shaky but admissible evidence is to be attacked by cross examination, contrary evidence, and attention to the burden of proof, not exclusion." The First Circuit reversed the exclusion of a weight-of-the-evidence causation opinion in Milward v. Acuity Specialty Products Group, Inc., 639 F.3d 11 (1st Cir. 2011), and the Federal Circuit treated many attacks on damages inputs as weight in Summit 6, LLC v. Samsung Electronics Co., 802 F.3d 1283 (Fed. Cir. 2015) and Apple Inc. v. Motorola, Inc., 757 F.3d 1286 (Fed. Cir. 2014). The other habit, visible in Paoli, Amorgianos, Elcock, Nease, and Sardis, demanded reliability at every step.

The 2023 note sided with the second habit by name, and the en banc Federal Circuit's EcoFactor decision shows a court of appeals correcting course: it reheard a case in which a panel had affirmed the admission of a royalty opinion, and held the opinion inadmissible under Rule 702(b). Some district courts still recite the old weight language, often by quoting pre-2023 circuit precedent that has not been formally revisited. The practical response is to build a deposition record that does not depend on which habit the judge has. If the expert concedes, in her own words, that she did not test the hypothesis, cannot identify the standard, or chose the rate without a method, the motion wins under either approach.

Other differences are worth knowing before you notice the deposition:

• Treating physicians and other non-retained experts. The Seventh Circuit requires a full report when a treating physician's causation opinion was formed outside the course of treatment, Meyers v. National Railroad Passenger Corp., 619 F.3d 729 (7th Cir. 2010), and so does the Ninth when the treater reviewed litigation materials from counsel, Goodman v. Staples the Office Superstore, LLC, 644 F.3d 817 (9th Cir. 2011). The Sixth Circuit allowed causation testimony without a report where the opinion was formed during treatment, Fielden v. CSX Transportation, Inc., 482 F.3d 866 (6th Cir. 2007). And failing to disclose a treater as an expert at all can end the case: in Musser v. Gentiva Health Services, 356 F.3d 751 (7th Cir. 2004), exclusion led straight to summary judgment.
• Qualifications. Most circuits read qualifications liberally, as in Pineda v. Ford Motor Co., 520 F.3d 237 (3d Cir. 2008), but the Federal Circuit has held it an abuse of discretion to admit technical testimony on infringement or invalidity from witnesses who are not qualified in the pertinent art, Sundance, Inc. v. DeMonte Fabricating Ltd., 550 F.3d 1356 (Fed. Cir. 2008) (a patent lawyer opining on obviousness) and HVLPO2, LLC v. Oxygen Frog, LLC, 949 F.3d 685 (Fed. Cir. 2020).
• Survey and class certification experts. Survey experts in trademark cases and damages modelers at class certification draw their own lines of authority; see Daubert Challenges to Consumer Survey Experts in Trademark Litigation and Class Certification and the Expert Battle, which discusses how Comcast Corp. v. Behrend, 569 U.S. 27 (2013) requires a damages model to measure only the damages attributable to the theory of liability.

Rule 30(b)(6) testimony versus expert testimony

Lawyers sometimes try to get expert opinions out of an organization's Fed. R. Civ. P. 30(b)(6) designee ("Describe all reasons the accused product does not infringe"), or to use the company's engineer as a cheap substitute for a retained expert. Both moves have limits. A Rule 30(b)(6) witness testifies to information known or reasonably available to the organization, and the organization must prepare the witness to do that, United States v. Taylor, 166 F.R.D. 356 (M.D.N.C. 1996). But "depositions, including 30(b)(6) depositions, are designed to discover facts, not contentions or legal theories," JPMorgan Chase Bank v. Liberty Mutual Insurance Co., 209 F.R.D. 361 (S.D.N.Y. 2002), and an organization does not have to produce a designee to deliver its experts' opinions in advance of their reports. Going the other way, an employee who will offer opinions based on specialized knowledge is an expert witness who must be disclosed under Rule 26(a)(2), with a (B) report if her duties regularly involve giving expert testimony and a (C) summary otherwise. The two depositions also bind differently: a 30(b)(6) designee speaks for the company, while an expert speaks for herself. For the corporate-deposition side, see Preparing and Defending a Rule 30(b)(6) Deposition and the Rule 30(b)(6) Deposition Preparation Checklist.

Taking the deposition: goals, structure, and technique

Eight goals, in order of importance

1. Lock the opinions. Get the expert to agree that the report states every opinion, that no further work is planned, and that nothing material was left out.
2. Close the doors. Establish what the expert is not offering: no opinion on infringement from the damages expert, no opinion on copying from the coding-style expert, no opinion on intent from anyone.
3. Expose the assumptions and the attorney-supplied facts. These are the Rule 26(b)(4)(C) exceptions, and they are where opinions are usually weakest.
4. Test the method. Testing, peer review, error rate, standards, acceptance, and the Kumho question of whether the expert would do the same work outside litigation.
5. Extract concessions. Points of agreement with your own expert, alternative explanations the expert did not rule out, and facts that cut against the opinion.
6. Show bias and compensation. Fees, hours, percentage of income from testifying, and repeat business with this firm or this client.
7. Pin down the reliance materials. What was considered, what was relied on, who selected it, and what the expert asked for and did not get.
8. Set up the motion and the trial cross. Clean question-and-answer pairs that a brief can quote and a video clip can show.

The funnel

Expert depositions work best as a series of funnels, one per opinion. Start wide and open ("Tell me everything you did to arrive at the 7 percent rate"), narrow with follow-ups ("What did you do after you selected the comparable licenses?"), and close with short leading questions that lock the answer ("So the only adjustment you made for the difference in technology was the 30 percent discount on page 61?"). Then ask the closing question that makes the funnel useful later: "Is there anything else you did to arrive at that rate?" The open stage is discovery; the closed stage is the record. Skipping the open stage leaves you guessing at trial; skipping the closed stage leaves you with a transcript of lectures no judge will read. The general technique is covered in The Art and Science of Depositions in Federal Civil Litigation and the Preparing to Take a Deposition Checklist.

Qualifications, prior testimony, and bias

Rule 26(a)(2)(B) requires a list of publications from the prior ten years and of cases in which the expert testified at trial or by deposition in the prior four. Read every item you can get. Ask about cases outside the four-year window, reports served in cases that settled before testimony, and any testimony since the report was signed. Bias discovery is legitimate but bounded. In Behler v. Hanlon, 199 F.R.D. 553 (D. Md. 2001), the court held that a defense medical examiner's work for insurers and defense lawyers was discoverable for bias impeachment, but that tax returns and total income were overkill; the percentage of gross income earned from expert work, and the pattern of retention, would let a jury assess bias without the intrusion. The cross that works on bias at trial is usually one clean exchange (rate, hours, total billed, percentage of income, number of prior engagements for this firm), so get those numbers cleanly at the deposition and move on.

Publications, treatises, and prior inconsistent testimony

Experts write. Find the expert's articles, slide decks, course materials, patents, blog posts, and prior reports, and look for the sentence that contradicts today's opinion. The sequence matters: commit the expert to the proposition first ("You agree that a regression with fewer than thirty observations is unreliable for this purpose?"), then confront with the prior statement, then ask for the explanation. If you confront first, the expert explains first, and the explanation becomes the record. Use the deposition to authenticate impeachment materials under Fed. R. Evid. 901 ("Is this a true copy of the article you published in 2019?") and to lay the Rule 803(18) foundation for the field's standard texts.

Hypotheticals and "would you change your opinion if"

An expert's opinion is only as good as its assumptions, and the jury, not the expert, decides whether the assumed facts are true. The most efficient way to make that point is the change question: "If the jury finds that the '417 patent is not essential to the standard, does your $212 million figure change? To what?" Each yes makes an assumption load-bearing, which helps the taking lawyer at trial. Each no is often better still, because an opinion that does not change when its premise disappears is an opinion that was not built on the premise. Hypotheticals must have a basis in the record to be usable at trial, so build them from documents and testimony already in the case.

The filibuster and the "I'd have to look" dodge

Some experts answer every question with a lecture; seven hours go quickly that way. Narrow the question, repeat it verbatim, and say "move to strike as nonresponsive" so the objection is preserved. Keep a log of the time consumed by nonresponsive answers, because that log is how you get more time under Rule 30(d)(1). For the expert who says "I'd have to look at my file," hand her the file, or the page, and wait. If the materials are not in the room, ask: "Sitting here today, can you identify any document that would change that answer?" A no closes the door; a yes tells you what to subpoena.

Building the Rule 702 record

For each opinion, the transcript should answer, in the expert's words: what the method is; where it comes from and who else uses it; whether it has been tested and with what error rate; what data went in and where each item came from; which assumptions were supplied by counsel; how the method was applied, step by step; which alternatives were considered and how each was ruled out; and what the opinion does not cover. Then stop. The temptation to argue with an expert about a concession you have just obtained is the most expensive temptation in the deposition room. You are not trying to win the argument with the witness; you are writing the motion.

Defending the deposition: protecting your own expert

Preparation sessions, and what the other side can learn about them

Preparation is legitimate and expected; scripting is not. The opinions must be the expert's own, and ABA Model Rule of Professional Conduct 3.4(b) forbids assisting a witness to testify falsely. Within that line, the work is substantial: re-reading the report, the opposing report, the key documents, and the expert's own prior testimony; mock cross-examination on the weakest opinion; and a session as long as the deposition itself, so the expert learns what hour six feels like. Assume the other side will ask how many sessions there were, who attended, how long they lasted, and what the expert reviewed. Communications with counsel in those sessions are protected by Rule 26(b)(4)(C) except for the three exceptions, so any fact or assumption counsel supplies in preparation is discoverable. Documents the expert reviews to refresh recollection can be ordered produced under Fed. R. Evid. 612. And anything the expert brings into the room, a cheat sheet or an annotated report, belongs to the other side the moment it appears. The rule for the expert is simple: bring nothing you would not hand to opposing counsel.

The report as script

A well-prepared expert answers from the report. For every opinion, she should be able to turn to the page, state the opinion in one sentence, and explain the method in three. When a question goes beyond the report, the truthful answer is usually "I was not asked to analyze that, and I have not formed an opinion on it." That answer protects the witness from being pushed into a new opinion on the fly, but it has a cost the defending lawyer must weigh: every disclaimer narrows what the expert can say at trial, and the other side will quote the disclaimers in a Rule 37(c)(1) motion if the trial testimony drifts. The goal is precision, not evasion. An expert who seems to be hiding behind the report looks worse to a jury than one who says plainly where her work stops.

Teaching the three exceptions

The expert needs to know, before the deposition, exactly which communications are open:

• Compensation. Rate, hours, invoices, the engagement letter, and any unpaid balance. Have the numbers ready; an expert who cannot say what she has billed looks either careless or coy.
• Facts or data counsel provided and the expert considered. Every document counsel sent, including the ones she skimmed and set aside. The considered-materials list in the report should be complete, and the expert should know how each item reached her.
• Assumptions counsel provided and the expert relied on. These should be listed in the report, ideally in a separate section, each with a sentence explaining why the expert considers it reasonable and what she did, if anything, to check it. An expert who can say "I was asked to assume the license term ended in 2027, and I confirmed that from Section 12.1 of the agreement" is in a far better position than one who says "counsel told me."

Objections, instructions, and redirect

The defending lawyer's tools are few and should be used sparingly. Object to form, briefly, and stop; speaking objections are prohibited by Rule 30(c)(2) and expose the lawyer to sanctions under Rule 30(d)(2). Instruct not to answer only to protect a privilege or work product (most often, a question asking what counsel said about a draft), to enforce a court order, or to present a Rule 30(d)(3) motion, and then make the motion promptly; Redwood v. Dobson shows what happens otherwise. Questioning your own expert at the end is a judgment call. With fact witnesses, defending lawyers usually ask nothing. With experts the calculus differs, because a Daubert motion may be decided on the papers, and a misleading answer left uncorrected may be quoted as the expert's last word. Ask a few short questions only if the record contains a real error or an answer that a misleading question produced, and only if you know what the expert will say.

Errata and supplementation

Fed. R. Civ. P. 30(e) gives the witness 30 days after notice that the transcript is available, if review was requested before the deposition ended, to sign a statement of changes "in form or substance" with the reasons for them. The circuits disagree about substance. The Seventh Circuit holds that a change "which actually contradicts the transcript is impermissible unless it can plausibly be represented as the correction of an error in transcription, such as dropping a 'not,'" Thorn v. Sundstrand Aerospace Corp., 207 F.3d 383 (7th Cir. 2000). The Ninth Circuit says Rule 30(e) is for corrective, not contradictory, changes and likens sham corrections to sham affidavits, Hambleton Bros. Lumber Co. v. Balkin Enterprises, Inc., 397 F.3d 1217 (9th Cir. 2005), and the Tenth Circuit agrees, Garcia v. Pueblo Country Club, 299 F.3d 1233 (10th Cir. 2002), and has applied the principle to an expert whose errata substantially qualified his testimony, BancFirst ex rel. Estate of M.J.H. v. Ford Motor Co., 422 F. App'x 663 (10th Cir. 2011). The Third Circuit takes a flexible, case-by-case approach and treats a missing statement of reasons as enough to strike a change, EBC, Inc. v. Clark Building Systems, Inc., 618 F.3d 253 (3d Cir. 2010), and some district courts are more permissive still, as in Aetna Inc. v. Express Scripts, Inc., 261 F.R.D. 72 (E.D. Pa. 2009). For an expert, the cleaner route to a substantive correction is usually a Rule 26(e) supplement explaining the error, paired with an offer to make the expert available for a short continued deposition at the retaining party's expense. The same logic governs declarations filed with summary judgment and Daubert briefing: a declaration that contradicts the deposition without explanation invites the sham affidavit doctrine that runs from Perma Research & Development Co. v. Singer Co., 410 F.2d 572 (2d Cir. 1969) through Cleveland v. Policy Management Systems Corp., 526 U.S. 795 (1999). The errata and designation mechanics are covered in depth in Using Depositions at Trial and on Summary Judgment.

Preparing for the Daubert hearing

The deposition is the first draft of the Daubert hearing. Read the transcript the way the judge will: looking for the questions the expert could not answer. Then decide whether to address the gaps with a declaration (consistent with the testimony, explaining rather than changing it), with live testimony at a Fed. R. Evid. 104(a) hearing, or by narrowing the opinions the expert will offer. Narrowing is underused. Withdrawing the one opinion the expert cannot defend often saves the three she can.

Special situations

Reliance material requests and Rule 45 subpoenas to experts

The report identifies what the expert considered; it does not usually attach the working files, and under Gillespie it does not have to. The taking lawyer gets the rest three ways: a Fed. R. Civ. P. 34 request to the retaining party for the expert's file, a document subpoena under Fed. R. Civ. P. 45 served with the deposition notice, or an agreed production protocol in the expert stipulation. Courts disagree about bare document subpoenas to the other side's retained experts. In Marsh v. Jackson, 141 F.R.D. 431 (W.D. Va. 1992), the court quashed subpoenas for two experts' entire files, holding that Rule 26(b)(4) still controls discovery from experts retained to testify and that a stand-alone Rule 45 subpoena could not be used to get around it, while noting that a subpoena served together with a deposition was permissible. Other courts allow the stand-alone subpoena. The safe course is to request the file from the party, serve the subpoena with the notice, and ask for production at least a week before the deposition so you are not reading spreadsheets at the table. Serve every subpoena on all parties under Rule 45(a)(4). For the mechanics, see Rule 45 Subpoenas to Nonparties.

Remote expert depositions

Under Rule 30(b)(4), the parties may stipulate, or the court may order, that a deposition be taken by remote means, and the deposition takes place where the witness answers. Remote expert depositions work well if the exhibit plan is serious: exhibits pre-marked and delivered sealed, or shared on a platform that logs what the witness sees; a stipulation that the witness is alone, has no messaging application open, and has only the materials listed; a camera framed so the witness's hands and desk are visible; and a backup audio line. The video record matters more than in a fact deposition, because a remote expert who looks off-screen before every answer makes a memorable clip at trial.

Foreign experts and the Hague Evidence Convention

A party's own retained expert who lives abroad is usually produced voluntarily, and the scheduling order can require it. When an expert must be deposed abroad, Fed. R. Civ. P. 28(b) allows depositions in a foreign country under an applicable treaty or convention, by letter of request (transmitted under 28 U.S.C. § 1781), on notice, or by commission. The Hague Evidence Convention is an available route but not a mandatory first resort for discovery from parties, Societe Nationale Industrielle Aerospatiale v. United States District Court, 482 U.S. 522 (1987). Some countries restrict or prohibit depositions on their territory even of willing witnesses, so check the State Department's country-specific judicial assistance information (travel.state.gov) before booking anyone's flight. For the cross-border toolkit, see Cross-Border Discovery Toolkit.

Using the deposition at trial and on summary judgment

An expert's deposition can be used at trial to contradict or impeach under Fed. R. Civ. P. 32(a)(2), and as substantive testimony if the witness is unavailable under Rule 32(a)(4), which includes a witness more than 100 miles from the place of trial unless the offering party procured the absence. Experts often qualify, which is why some lawyers take trial-preservation depositions of their own experts and why the taking lawyer should assume any expert deposition may be played to the jury. On summary judgment, an expert declaration must be admissible under Fed. R. Civ. P. 56(c)(4) and Rule 702, and the moving party can point to the expert's deposition concessions to show the absence of a genuine dispute under Celotex Corp. v. Catrett, 477 U.S. 317 (1986). Designation practice, objections to designations, and video editing are covered in Designating and Playing Deposition Testimony at Trial and the Deposition Use Toolkit; see also Summary Judgment Under Rule 56.

Worked example 1: deposing a reasonable-royalty expert in a patent case

Return to the report from the opening. Kestrel Networks sues Brightwave Semiconductor for infringing the '417 patent, which claims a beamforming technique that Kestrel says is used in Brightwave's Wi-Fi chipsets. Kestrel's damages expert, Dr. Whitlock, opines that a reasonable royalty is 1.2 percent of chipset revenue, or $212 million. You represent Brightwave, and the scheduling order gives you 21 days between rebuttal reports and the close of expert depositions.

Before the deposition. You serve a Rule 34 request and a Rule 45 subpoena for the expert's working files and get her spreadsheet model. It shows the 1.2 percent rate came from three licenses: two lump-sum settlements of earlier suits on the '417 patent and one 2016 running-royalty license covering a portfolio of 40 patents. The model applies a "technical contribution" factor of 40 percent, attributed in a footnote to a conversation with Kestrel's technical expert. And page 61 contains the sentence about assuming standard essentiality.

The deposition. The outline runs in five funnels. First, the lock: Dr. Whitlock confirms that her report contains all her opinions, that she plans no further work, and that her rate opinion depends on the three licenses and nothing else. Second, the exceptions: she identifies the assumptions counsel supplied (essentiality, a 2015 hypothetical negotiation date, and that every accused unit practices the claims) and the documents counsel sent. Third, the conversion: asked how she turned two lump sums into a per-unit rate, she points to the licenses' "whereas" recitals, which describe a rate the licensees never agreed to pay. You ask her to list every fact supporting the conversion, then ask whether there is anything else; there is not. That is the EcoFactor record. Fourth, the 40 percent factor: she cannot say how the technical expert derived it and agrees she did no independent analysis, which is the Dura mouthpiece problem and the Exmark explanation problem at once. Fifth, the change questions: if the '417 patent is not essential, her rate does not change. Asked how her number separates the value of the technique from the value of its inclusion in the standard, she says the licenses "already reflect" that. Under Ericsson, that answer is a gift.

What you do not do. You do not argue with her about discount rates, ask her to agree that her opinion is unreliable, or show her your own expert's report. You leave with forty pages of short answers and a Rule 702 motion that writes itself under subsections (b) and (d). The court excludes the rate opinion, leaves the royalty base, and orders a supplemental report limited to correcting the error; the case settles four weeks later. For the damages doctrine behind each question, see Proving and Attacking Patent Damages.

Worked example 2: defending a software engineer expert in a copyright case

Harbor Systems sues Lumen Analytics, alleging that Lumen's data-pipeline product copies the structure and code of Harbor's software. You represent Lumen. Your expert, Dr. Nandakumar, is a software engineer who performed an abstraction-filtration-comparison analysis under Computer Associates International, Inc. v. Altai, Inc., 982 F.2d 693 (2d Cir. 1992) and Gates Rubber Co. v. Bando Chemical Industries, Ltd., 9 F.3d 823 (10th Cir. 1993) and concluded that the similarities are dictated by efficiency, external constraints, open-source libraries, and public interfaces, and so are unprotectable under 17 U.S.C. § 102(b).

Structure before substance. Months earlier, Lumen had retained a different engineer as a consultant to investigate the claim before suit. Because of Yeda, you kept that consultant out of the testifying role and out of Dr. Nandakumar's file, and you can say so truthfully at the deposition. You also confirmed that Dr. Nandakumar's tool outputs, comparison logs, and notes were preserved, because Fidelity makes clear that "irrelevant" working materials must still be retained if she considered them.

Preparation. You spend two sessions on three predictable lines of attack. First, scope: she compared selected modules rather than the entire codebase, so she must explain the selection criteria and why they are the ones a forensic engineer would use outside litigation. Second, subjectivity: Harbor will call the filtration step "judgment," so she should tie each filtration category to published criteria and identify where another engineer could check her work. Third, the conversations she had with Lumen's developers about why the code was written as it was. Those communications are not protected by Rule 26(b)(4)(C), which covers only counsel, so she should know exactly whom she spoke with and what she learned, and her report should list those interviews as facts considered.

At the deposition. Harbor's counsel asks what you said about her second draft. You instruct her not to answer under Rule 26(b)(4)(B) and (C) and state the basis in one sentence. Harbor's counsel then asks which files you asked her to compare; that is facts or data provided by counsel, and she answers fully. Asked whether an ordinary user would find the two products substantially similar, she says she was not asked to address that and has no opinion. That answer matters doctrinally: in the Second Circuit, Arnstein v. Porter, 154 F.2d 464 (2d Cir. 1946) confined expert dissection to the question of copying, and in the Ninth, Sid & Marty Krofft Television Productions, Inc. v. McDonald's Corp., 562 F.2d 1157 (9th Cir. 1977) allowed experts on the extrinsic test but not the intrinsic one. Software cases soften those limits (Altai left room for expert help on technical works, and Dawson v. Hinshaw Music Inc., 905 F.2d 731 (4th Cir. 1990) asks about the work's intended audience), but staying inside the report keeps the testimony where the law plainly allows it. You ask no questions at the end.

Afterward. Reading the transcript, she finds she gave a 2019 commit date that the repository log shows was 2021. The errata sheet corrects it with the reason ("misstatement; see repository log entry"), which is the kind of change every circuit accepts. Harbor's Daubert motion argues that her filtration is subjective; the court denies it because the transcript shows criteria, sources, and a method another engineer could replicate. For the substantive copyright framework, see Proving Copyright Infringement and the Copyright Infringement Litigation Toolkit.

Costs and practical realities

Expert depositions are expensive on both sides of the table. Retained technical and economic experts commonly bill several hundred to well over a thousand dollars an hour, and a single deposition, counting the expert's preparation, the testimony day, the transcript, and video, can cost the retaining side tens of thousands of dollars before the deposing side pays a dollar of the Rule 26(b)(4)(E) fee. The taking lawyer's preparation for a major expert typically runs one to three weeks of attorney time: reading the report, the materials considered, prior testimony, and publications, and working with your own expert to find the soft spots. Expert discovery windows are short, often 30 to 60 days after rebuttal reports, so the outline and the subpoenas should be drafted while the rebuttal report is still being written. A practical budgeting rule: the expert deposition that leads to a successful Daubert motion is the cheapest litigation spend in the case, and the one taken without a plan is among the most wasteful.

Common mistakes

Taking side

• Arguing with the expert instead of extracting the concession and moving on.
• Never asking "Are those all of your opinions?" and "Is there anything else?"
• Asking about drafts and attorney comments instead of the three exceptions.
• Reading the working files for the first time at the deposition.
• Long, compound questions that produce long, unusable answers, and no motion to strike as nonresponsive.
• Saving every impeachment for trial without first locking the testimony and authenticating the documents.

Defending side

• Letting the consultant become the testifier without thinking about Yeda.
• Allowing the expert to bring notes or an annotated report into the room.
• An assumptions section that says only "counsel instructed me to assume."
• Coaching objections, and instructions not to answer that no rule supports.
• Trying to repair a bad answer through a contradictory errata sheet instead of a disclosed supplement.
• Over-disclaiming at the deposition, then trying to expand the testimony at trial.

Frequently asked questions

Can I get the other side's draft expert reports? Not ordinarily. Rule 26(b)(4)(B) protects drafts in any form, and overcoming the protection requires a showing of substantial need that courts rarely find. You can get the expert's notes, working files, testing, and everything she considered, which is usually more useful than the drafts were.

What may I ask about the expert's conversations with the lawyer who hired her? Three things: compensation, the facts or data the lawyer provided that she considered, and the assumptions the lawyer provided that she relied on. Her conversations with anyone else, including the client's employees and other experts, are not protected by Rule 26(b)(4)(C).

Who pays for the expert's time at the deposition? The party taking the deposition pays a reasonable fee for the time spent responding, unless manifest injustice would result. Whether that includes preparation time varies by court, so agree on it in writing beforehand. The expert's fees are generally not recoverable as costs at the end of the case unless a statute or contract allows it.

How long can an expert deposition last? One day of seven hours on the record, unless the parties stipulate or the court orders more. Courts regularly allow more for experts who address several patents, products, or reports; negotiate it in the scheduling order.

My expert made a mistake at the deposition. Can she fix it? A transcription error or a misstatement of a date can go on the errata sheet with a reason. A substantive change is risky; several circuits strike errata that contradict the testimony. The better course is usually a Rule 26(e) supplement that explains the correction, with an offer of a short continued deposition.

Can I depose the other side's consulting expert? Only on a showing of exceptional circumstances, such as destructive testing that left nothing for anyone else to examine. If the consultant is later designated to testify, the protection largely disappears for anything bearing on the testimony.

Should I always depose the other side's expert? Almost always. The cases for skipping it (a hopeless report you can attack on its face, or a strategy that depends on surprise at trial) are narrower than they look, because Rule 702 motions are won on the expert's own concessions and an undeposed expert can expand her testimony at trial in ways that are hard to police.

Did the 2023 amendment change what I should ask? It changed the emphasis. Sufficiency of the facts and the reliability of the application are admissibility questions that the proponent must prove by a preponderance of the evidence, opinion by opinion. Build the record element by element, and get the expert to identify everything she relied on, because the question under Rule 702(b) is whether those facts suffice.

Practical takeaways

• The deposition serves two later events, the Rule 702 motion and the trial cross. Plan every chapter backward from one or the other.
• Ask about the three Rule 26(b)(4)(C) exceptions, never about drafts. Assumptions supplied by counsel are where opinions break.
• Lock the opinions and close the doors at the start and again at the end: all opinions, no further work, nothing else relied on.
• Walk each opinion one step at a time. Paoli's "any step" principle and the amended Rule 702(d) reward the lawyer who finds the single unsupported inference.
• For the defending side, structure beats rescue: separate consultants from testifiers, preserve the file, write a real assumptions section, and prepare the expert to answer from the report.
• Fix substantive errors through disclosed supplementation, not contradictory errata.
• Get the reliance materials and working files well before the deposition, by Rule 34 request and by subpoena served with the notice.

This document is general information, not legal advice for any particular situation; the law changes, and the facts matter.

Related Documents

Related Articles

• Expert Witnesses After the 2023 Amendment to Rule 702: Daubert, Disclosure, and Cross-Examination: the amendment, the trilogy, and the motion practice this deposition feeds.
• Using Depositions at Trial and on Summary Judgment: Rule 32, Designations, Errata Sheets, and Impeachment: what happens to the transcript after the deposition ends.
• Patent Damages: Reasonable Royalties, Lost Profits, Apportionment, and Enhancement: the doctrine behind the royalty expert questions.
• Proving Copyright Infringement: Access, Substantial Similarity, and the Tests Courts Actually Use: where software experts fit in the similarity analysis.
• Trade Secret Damages and Remedies: unjust enrichment and royalty experts in misappropriation cases.
• Class Certification and the Expert Battle: Daubert at the certification stage.
• The Art and Science of Depositions in Federal Civil Litigation: general deposition technique.
• The Art of Defending Depositions in Federal Court: objections, instructions, and witness protection.
• Rule 45 Subpoenas to Nonparties: serving and fighting the subpoena for the expert's file.

Related Guides

• Taking and Defending an Expert Deposition: A Practical Guide: the step-by-step companion to this article.
• Proving and Attacking Patent Damages: building and dismantling royalty models.
• Designating and Playing Deposition Testimony at Trial: designations, counter-designations, and video.
• Daubert Challenges to Consumer Survey Experts in Trademark Litigation: survey experts and their particular vulnerabilities.
• Preparing and Defending a Rule 30(b)(6) Deposition: the corporate deposition that experts are sometimes confused with.

Related Checklists

• Expert Deposition Preparation Checklist: task lists for both sides of the table.
• Expert Disclosure and Daubert Challenge Checklist: disclosures, deadlines, and the motion.
• Preparing to Take a Deposition Checklist: the general taking checklist.
• Preparing a Privilege Log: logging work product withheld from expert productions.

Related Toolkits

• Expert Deposition Toolkit: Outline Frameworks, Reliance Material Requests, and Rule 26 Protection Maps: outlines, subpoena riders, and protection maps.
• Expert Witness Toolkit: selecting, retaining, and managing experts from start to finish.
• Patent Damages Toolkit: royalty models, reports, and Daubert motions.
• Copyright Infringement Litigation Toolkit: similarity charts and filtration analyses.
• Deposition Practice Toolkit: the full deposition workflow in federal court.
• Discovery Toolkit: the broader discovery framework.