There are many reasons why expert witnesses are increasingly being excluded from testifying.

Attorney Joshua E. Garner, special counsel at the U.S. Department of Justice writing for SEAK, Inc. explains with the following article:


Joshua E. Gardner


In federal court, experts tend to get excluded for one of two reasons: either they fail to comply with the disclosure requirements under the Federal Rules of Civil Procedure or they fail to meet the standards for admissibility set forth in the Federal Rules of Evidence.
As discussed in more detail below, in most cases an expert must prepare a report that provides the opinions she intends to offer, the facts, data and methodology used in reaching those opinions, her qualifications and list of prior deposition and trial testimony, and the disclosure of compensation. This disclosure, as well as any supplementation, must be done in a timely manner. Furthermore, to be admissible, the district court, acting as a gatekeeper, must determine that the expert is qualified, possesses scientific, technical or other specialized knowledge, and is offering expert testimony that is both reliable and relevant. Below is a detailed discussion of these requirements, with illustrations included as appropriate.


A. Required disclosures: For many types of experts, the following information must be disclosed in a written report:

1. “[A] complete statement of all opinions the witness will express and the basis and reasons for them;”

2. “[T]he facts or data considered by the witness in forming them;”

3. “[A]ny exhibits that will be used to summarize or support them;”

4. “[T]he witness’s qualifications, including a list of all publications authored in the previous 10 years;”

5. “[A] list of all other cases in which, during the previous 4 years, the witness testified as an expert at trial or by deposition;” and

6. “[A] statement of the compensation to be paid for the study and testimony in the case.” See Fed. R. Civ. P. 26(a)(2)(B)(i)-(vi).

B. Timing of expert reports: Where the court enters a pretrial order governing the submission of expert reports, that order controls the determination as to whether the report submission is timely. See Akeva, LLC
v. Mizuno Corp., 212 F.R.D. 306, 309-10 (M.D.N.C. 2002) (holding that where discovery plan did not contemplate rebuttal reports, party was not entitled to submit rebuttal report). In the absence of a court order setting a time for disclosure, a party must disclose an expert report at least 90 days before the date set for trial or for the case to be ready for trial. Fed. R. Civ. P. 26(a)(2)(D)(i). Expert reports that are “intended solely to contradict or rebut evidence on the same subject matter identified by another party” is due 30 days after the initial report. See Fed. R. Civ. P. 26(a)(2)(D)(ii).

C. Supplementation of expert opinions: An expert must supplement if a party learns that the report, in some material respect, is incomplete or incorrect, and if the additional or corrective information has not otherwise been made known to the other parties during the discovery process or in writing.

1. For experts, the duty to supplement extends both to information contained in the report and to information given during the expert’s deposition. Disclosures of supplemental information must be made by the deadline for the party’s pretrial disclosures. See Fed. R. Civ. P. 26(a)(2)(E) & 26(e)(1)-(2).

2. However, rebuttal opinions are not the same thing as supplementation of existing opinions, and rebuttal opinions must be disclosed consistent with the court’s pretrial order or otherwise be made in accordance with Rule 26. See Covington v. Memphis Publ’g Co., No. 05-2474, 2007 WL 4615978, at *3-4 (W.D. Tenn. Oct. 16, 2007) (striking expert report that sought to rebut opposing expert’s opinions rather than supplementation because rebuttal report was untimely); Sandata Tech., Inc. v. Infocrossing, Inc., No. 05-09546, 2007 WL 4157163, at *5 (S.D.N.Y. Nov. 16, 2007) (holding that new expert report was considered rebuttal rather than supplementation where “nearly all of the discussion . . . serves as a response to various assertions made by [the other party’s] expert.”); Palmer v. Asarco, Inc., No. 03-0498, 2007 WL 2254343, at *3 (N.D. Okla. Aug. 3, 2007) (“Although parties are permitted to supplement expert disclosures, Rule 26(e) ‘does not give license to sandbag one’s opponent with claims and issues which should have been included in the expert witness’ report.’”) (citation omitted).

D. Consequences for failure to either timely or completely disclose: Courts have wide latitude in deciding what remedy to impose for a deficient or late report, including, among other things, requiring supplementation, a new deposition at the expense of the proponent of the expert, or exclusion of the expert’s opinions. See Fed. R. Civ. P. 37(c)(1) (the failure to disclose expert testimony may result in the exclusion of that testimony in the absence of a showing that the proponent of the expert testimony was substantially justified in failing to disclose the testimony or that the failure to disclose was harmless); see also Connelly v. H.O. Wolding, Inc., No. 06-5129, 2007 WL 2750595, at *2 (W.D. Mo. Sept. 18, 2007) (striking rebuttal expert affidavit that failed to provide, among other things, data and information considered
by expert). Exclusion may be appropriate even in the absence of prejudice to the opposing party. See Akeva, LLC v. Mizuno Corp., 212 F.R.D. 306, 311 (M.D.N.C. 2002) (“The factors involving docket control planning are sufficiently important to alone justify the exclusion of an untimely disclosed expert report or opinion even in [the] absence of prejudice to the opposing party.”); Meijer, Inc. v. Warner Chilcott Holdings Co., III, Ltd., 246 F.R.D. 293, n. 18 (D.D.C. 2007) (refusing to consider rebuttal affidavit that went beyond the scope of original affidavit); Trilogy Commc’ns, Inc. v. Times Fiber Commc’ns, Inc., 109 F.3d 739, 744-45 (Fed. Cir. 1997) (affirming exclusion of expert rebuttal affidavit where submission was after deadline for expert reports and the affidavit contained new opinions and information).


A. To be admissible, the court, acting as gatekeeping, must make the following determinations before the expert is permitted to provide her opinions:

1. The expert must be qualified, which may be by knowledge, skill, experience, training or education;

a. This requirement is intended to broaden the bases for an expert’s qualifications beyond education.

b. In some fields, experience is the predominant, if not sole, basis for reliable testimony. See, e.g., United States v. Jones, 107 F.3d 1147 (6th Cir. 1997) (holding that it was not abuse of discretion in admitting testimony of handwriting examiner who had years of practical experience and extensive training, and who explained his methodology in detail).

c. However, when an expert’s opinion is based solely or predominantly upon experience, the expert must explain how that experience lends to the conclusion reached, why that experience is a sufficient basis for the opinion, and how that experience is reliably applied to the facts. 2000 Advisory Committee Notes, Fed. R. Evid. 702; Marvel Characters, Inc. v. Kirby, 726 F.3d 119, 135-36 (2d Cir. 2013) (recognizing that an expert historian could be admissible under certain circumstances but affirming exclusion of expert historians who based opinions largely on hearsay statements by artists and speculated on the motivations and made credibility determinations of other witnesses).

d. The more subjective and controversial the expert’s opinion, the more likely the opinion will be excluded as unreliable. See O’Conner v. Commonwealth Edison Co., 13 F.3d 1090 (7th Cir. 1994) (expert testimony based on a completely subjective methodology held properly excluded).

e. One issue that sometimes arises in connection with an expert’s qualifications is whether there is “fit” between an expert’s expertise and the opinions the expert seeks to offer. See Radio Sys. Corp. v. Lalor, No. C10-828RSL, 2014 WL 4626298, at *2-3 (W.D. Wash. Sept. 12, 2014) (holding that expert who had “significant credentials and experience in computer science and digital processing,” there was no relationship to this experience and “the configuration and construction of the housing of an animal collar”);

2. The expert possesses “scientific, technical, or other specialized knowledge”

a. Henderson v. GMAC Mortg. Corp., 347 Fed. App’x. 299, 301 (9th Cir. 2009) (affirming exclusion of expert that “provided little information about where and when he obtained his education and training, his conclusions lacked factual support, and the opinions he provided required no scientific, technical, or other specialized knowledge.”)

b. Paquin v. Fed. Nat’l Mortg. Ass’n, 119 F.3d 23, 33 (D.C. Cir. 1997) (holding that witnesses who testified on behalf of plaintiff regarding plaintiff’s alleged discrimination were not entitled to expert fees because they only had personal knowledge and lacked any scientific, technical or other specialized knowledge).

3. The expert will help the trier of fact to understand the evidence or determine a fact in issue;

a. Is the expert offering opinions that are relevant to the issues in the case?

i) Camp v. Lockheed Martin Corp., No. 97-1938, 1998 WL 966002, at *3 (S.D. Tex. Dec. 29, 1998) (excluding industrial psychologist’s opinion that “unconscious age stereotyping could have influenced the decision” because “while perhaps of considerable interest to psychologists and sociologists, is not relevant to the issue whether [defendant] intentionally discriminated against [plaintiff]”).

ii) United States v. Szabo, 760 F.3d 997, 1001 n. 2 (9th Cir. 2014) (affirming exclusion of expert testimony concerning defendant’s diminished capacity on relevance grounds where diminished capacity defense was not available for general intent crime).

iii) Faulkner v. Wausau Bus. Ins. Co., 571 Fed. App’x 566, 569 (9th Cir. 2014) (affirming exclusion of expert on insurance claims handling on relevance grounds where expert did not review any of the insurance company’s claims handling documents).

iv) United States v. Dixon, 413 F.3d 520, 523-24 (5th Cir. 2005) (affirming exclusion of expert who would testify to criminal defendant’s subjective belief of duress as irrelevant because duress required an objective analysis).

b. Is the expert offering legal opinions?

i) In re Initial Pub. Offering Sec. Litig., 174 F. Supp. 2d 61, 64 (S.D.N.Y. 2001) (excluding expert’s opinion regarding whether recusal was appropriate based upon application of statute because it constituted legal conclusion).

ii) Lira v. Cate, No. 00-0905, 2010 WL 727979, at *4 n.5 (N.D.
Cal. Feb. 26, 2010) (excluding expert testimony “regarding the appropriate rates under the PLRA [and] whether a multiplier is authorized by the PLRA” as constituting improper legal opinions).

iii) United States v. Baca, 610 F. Supp. 2d 1203, 1220 (E.D. Cal. 2009) (excluding expert opinion that item was a “cultural resource” for purposes of a statute because it constituted a legal opinion).

iv) Burkhart v. Wash. Metro. Area Transit Auth., 112 F.3d 1207, 1213-14 (D.C. Cir. 1997) (affirming exclusion of expert who opined that the defendant violated the ADA, because it constituted an impermissible legal conclusion).

c. Is the expert offering opinions that a lay person could offer?

i) United States v. Lespier, 725 F.3d 437, 449 (4th Cir. 2013) (affirming exclusion of psychologist’s testimony about effects of sleep deprivation and holding that testimony concerning obvious matters are not helpful to the trier of fact under Federal Rule 702).

ii) United States v. Grizaffi, 471 F.2d 69, 74 (7th Cir. 1972) (affirming exclusion of accounting expert who simply made arithmetical computations based on data provided by counsel where such information was within the competence of the jurors).

4. The expert’s opinions are based on “sufficient facts or data”;

a. Lang v. Kohl’s Food Stores, Inc., 217 F.3d 919, 923-24 (7th Cir. 2000) (holding that an expert that opined on whether a plaintiff could perform the essential functions of a store clerk failed to consider sufficient facts or data when he only viewed a list of clerk duties identifying objectives without any analysis of what clerks actually did to meet those objectives).

b. Munoz v. Orr, 200 F.3d 291, 301 (5th Cir. 2000) (rejecting Title VII disparate impact claim where statistical analysis “fail[ed] to consider other variables such as education and experience as explanations for any observed discrepancy between promotion rates”).

c. Tagatz v. Marquette Univ., 861 F.2d 1040, 1045 (7th Cir. 1988) (rejecting Title VII claim because failure to control for other explanatory variables makes an expert’s table “essentially worthless”).

d. Garcia v. Johanns, 444 F.3d 625, 635 (D.C. Cir. 2006) (rejecting statistical analyses as “analytically flawed because they did not incorporate key relevant variables connecting disparate impact to loan decisionmaking criteria”)

e. Smith v. Ford Motor Co., No. 2:08-cv-630, 2013 WL 214378, at *2 (D. Utah Jan. 18, 2013) (excluding expert opinion that “every exposure” to asbestos may cause mesothelioma where expert based opinion upon the lack of sufficient facts and data to establish the minimum dosage necessary to cause cancer in humans).

f. Where an expert relies exclusively upon counsel for facts and data, and does nothing to verify those facts, this factor, coupled with other deficiencies, may subject an expert to exclusion. See, e.g., Munoz v. Orr, 200 F.3d 291, 301-02 (5th Cir. 2000) (affirming exclusion of expert witness in disparate impact case who started from the assumption that discrimination had occurred, made a number of mathematical errors, failed to consider important variables, and relied upon information provided by counsel and failed to verify it).

5. The expert’s opinions are the product of reliable principles and methods; and

a. The assessment of reliability is flexible and based upon a number of non-exclusive factors, including, among other things:

(1) Whether the scientific theory or technique can be (and has been) tested;

(2) whether the theory or technique has been subjected to peer review and publication;

(3) whether there is a known or potential error rate; and
(4) whether the theory or technique is generally accepted in the relevant scientific community.

Mukhtar v. Cal. State Univ., 299 F.3d 1053, 1064 (9th Cir. 2002).

b. The trial court has broad latitude to determine which factors are appropriate for consideration in any given case. Kumho Tire Co. v. Carmichael, 526 U.S. 137, 153 (1999).

c. “Publication, which is an element of peer review, ‘is not a sine qua non of admissibility,’” it may suggest “good science.” Oddi v. Ford Motor Co., 234 F.3d 136, 145 (3d Cir. 2000) (quoting Daubert, 509 U.S. at 593); see Zaremba v. Gen. Motors Corp., 360 F.3d 355, 358 (2d Cir. 2004) (affirming trial court’s exclusion of expert where expert had not subjected methodology to peer review or publication).

d. Similarly, “[w]idespread acceptance can be an important factor in ruling particular evidence admissible, and a known technique which has been able to attract only minimal support with the community may properly be viewed with skepticism.” Oddi v. Ford Motor Co., 234 F.3d 136, 145 (3d Cir. 2000) (quoting Daubert, 509 U.S. at 594); see Zaremba v. Gen. Motors Corp., 360 F.3d 355, 358 (2d Cir. 2004) (affirming trial court’s exclusion of expert where party tendering expert failed to demonstrate that expert’s opinion or methodology was generally accepted).

e. Reliance upon “expertise” or curriculum vitae, by itself, is not a sufficient method for purposes of admissibility. Zenith Elecs. Corp. v. WH-TV Broad. Corp., 395 F.3d 416, 418 (7th Cir. 2005) (holding that the expert “all but conceded that he had not applied ‘reliable principles and methods’. Asked repeatedly during his deposition what methods he had used to generate projections, [the expert] repeatedly answered ‘my expertise’ or some variant (‘my industry expertise’, ‘[my] awareness,’ and ‘my curriculum vitae’)—which is to say that he either had no method or could not describe one. He was relying on intuition, which won’t do.”).

f. The failure of the expert to test a hypothesis may be grounds for exclusion. Norris v. Baxter Healthcare Corp., 397 F.3d 878, 887 (10th Cir. 2005) (“[A]t best, silicone- associated connective tissue disease is an untested hypothesis. At worst, the link has been tested and found to be untenable. Therefore, there is no scientific basis for any expert testimony as to its specific presence in Plaintiff.”); Tamraz v. Lincoln Elec. Co., 620 F.3d 665, 677 (6th Cir. 2010) (reversing admission of hypothesis expert opinion and observing that “what science treats as a useful but untested hypothesis the law should generally treat as inadmissible speculation”); Brooks v. Outboard Marine Corp., 234 F.3d 89, 91–92 (2d Cir. 2000)( “[F]ailure to test a theory of causation can justify a trial court’s exclusion of the expert’s testimony.”); In re Breast Implant Litig., 11 F. Supp. 2d 1217, 1228 (D. Colo. 1998) (“An
untested hypothesis cannot be a scientifically reliable basis for an opinion on causation.”); Call v. Harrison, No.
5:12cv00008, 2012 WL 5993732, at *3 (W.D. Va. Nov.
30, 2012) (excluding opinion that was “an untested hypothesis” and stating that “[a]s such, it is far too unreliable to be admitted as an expert opinion”); In re Denture Cream Prods. Liab. Litig., 795 F. Supp. 2d 1345, 1367 (S.D. Fla. 2011) (excluding causation testimony because “In short, taking everything together, there is enough data in the scientific literature to hypothesize causation, but not to infer it. Hypotheses are verified by testing, not by submitting them to lay juries for a vote.”); Hall v. Baxter Healthcare Corp., 947 F. Supp. 1387, 1402 (D. Or. 1996) (excluding expert testimony on the ground that it was “an untested hypothesis”); Allstate Ins. Co. v. Ford Motor Co., No. CV–08–2276, 2010 WL 1654145, at *7 (D.
Ariz. Apr. 21, 2010) (excluding “untested hypothesis” because “testing the hypothesis is an essential step in [] the scientific method”).
g. The focus on methodology is “not [on] the correctness of the expert’s conclusions but the soundness of his methodology.” Primiano v. Cook, 598 F.3d 558, 564 (9th Cir. 2010) (citation omitted).

h. Kumho Tire Co. v. Carmichael, 526 U.S. 137, 153 (1999) (affirming trial court’s exclusion of accident reconstruction expert and noting that, despite the trial court’s acceptance of expert’s qualifications, the expert lacked a reliable methodology).

6. The expert has reliably applied the principles and methods to the facts of the case. See Fed. R. Evid. 702.

a. Gen. Elec. Co. v. Joiner, 522 U.S. 136, 146 (1997) (“[N]othing in either Daubert or the Federal Rules of Evidence requires a district court to admit opinion evidence that is connected to existing data only by the ipse dixit of the expert. A court may conclude that there is simply too great an analytical gap between the data and the opinion proffered.”)

B. Expert testimony that is cumulative may be subject to exclusion.
Where a party seeks to offer multiple experts providing the same opinion, the court may limit the party to a single expert on that opinion. See, e.g., Aetna Cas. & Sur. Co. v. Guynes, 713 F.2d 1187, 1193 (5th Cir. 1983) (affirming trial court’s exclusion of expert on grounds of cumulativeness); Washington v.
Greenfield, No. 86-930, 1986 WL 15758, at *1-2 (D.D.C. Oct. 15, 1986)
(excluding expert that presented “very similar testimony” to other expert and where both experts possessed the same credentials and board certification). Similarly, exclusion is appropriate where one expert intends to vouch for another expert or restate another expert’s opinions. See, e.g., Tunis Bros. Co. v. Ford Motor Co., 124 F.R.D. 95, 98 (E.D. Pa. 1989) (holding the exclusion of expert was appropriate where expert intended to vouch for other expert, which usurped the role of the jury); Robert S. v. Stetson Sch., Inc., 256 F.3d 159, 170 (3d Cir. 2001) (upholding exclusion of expert on cumulativeness grounds where two other experts testified at length about same issue); In re Air Crash Disaster, 86 F.3d 498, 527 (6th Cir. 1996) (affirming exclusion of “me too” expert where excluded expert did not offer new “angle or argument”); Tran v. Toyota Motor Corp., 420 F.3d 1310, 1315 (11th Cir. 2005) (affirming exclusion of expert witness where he and other expert relied upon same evidence in forming their opinions, the opinions were the same, and the experts’ qualifications were generally the same).

C. The Court is the gatekeeper of admissible expert testimony.

1. The district court, rather than the jury, serves as the gatekeeper for the admissibility of all expert testimony. See Kumho Tire Co. v. Carmichael, 526
U.S. 137, 147-49 (1999) (holding that “gatekeeper” function applies to all expert testimony); Barabin v. AstenJohnson, Inc., 700 F.3d 428, 433 (9th Cir. 2012) (holding that it was reversible error where district court failed to exercise gatekeeping obligation in assessing whether expert testimony was relevant and reliable).

2. Although the proponent of expert testimony has the burden of establishing admissibility, Daubert v. Merrell Dow Pharms., 509 U.S. 579, 592 n.10 (1993); Meister v. Medical Engineering Group, 267 F.3d 1123, 365
n.9 (D.C. Cir. 2001), courts tend to apply a presumption in favor of admissibility and “the rejection of expert testimony is the exception rather than the rule.” 2000 Advisory Committee Notes, Fed. R. Evid. 702.

a. The Supreme Court has recognized that cross-examination, the presentation of contrary evidence, and jury instructions addressing the burden of proof are tools that often may be employed to address shaky expert testimony, and that these tools are favored over exclusion. See Daubert v. Merrell Dow Pharm., 509 U.S. 579, 596 (1993).

b. Courts draw a distinction between the weight to be afforded to the expert’s opinions and the admissibility of the expert’s opinions, although the line between these two things may not
always be clear. See Adams v. Lab. Corp. of Am., 760 F.3d 1322, 1334 (11th Cir. 2014) (“At most, LabCorp established that there is an unspecified level of risk that [the expert’s] assessment might have been biased, and that she had not sought to exclude the possibility of bias by conducting a blinded review. The risk of bias would mean, at most, that [the expert’s]testimony is to some extent ‘shaky,’ and shakiness goes to the weight of her testimony, not its admissibility.”); Johnson v. Mead Johnson & Co., 754 F.3d 557, 563 (8th Cir. 2014) (holding that challenges to differential diagnosis opinion based on the failure to rule out all possible causes of illness went to weight rather than admissibility); Apple, Inc. v. Motorola, Inc., 757 F.3d 1286, 1320 (Fed. Cir. 2014) (holding that challenge to an expert’s use a of a particular benchmark went to weight of expert’s opinion rather than admissibility); McLean v. 988011 Ontario, Ltd., 224 F.3d 797, 801 (6th Cir. 2000) (holding that mere “weaknesses in the factual basis of an expert witness’ opinion . . . bear on the weight of the evidence rather than on its admissibility.”) (citation omitted).

3. The application of Daubert in bench trials.

a. A number of courts have held that the gatekeeping function has less importance in bench trials. In re Tex. Grand Prairie Hotel Realty, LLC, 710 F.3d 324, 329 (5th Cir. 2013) (stating that “most of the safeguards provided for in Daubert are not as essential in a case . . . where a district judge sits as the trier of fact . . .”) (citation omitted); David E. Watson, P.C. v. United States, 668 F.3d 1008, 1015 (8th Cir. 2012) (“When the district court sits as the finder of fact, ‘[t]here is less need for the gatekeeper to keep the gate when the gatekeeper is keeping the gate only for himself.’”) (citation omitted); In re Salem, 465 F.3d 767, 777 (7th Cir. 2006) (“Where the gatekeeper and the factfinder are one and the same—that is, the judge—the need to make such decisions prior to hearing the testimony is lessened.”).

b. Nevertheless, even in a bench trial, the district court must make a determination that the expert’s testimony is both reliable and relevant. See Metavante Corp. v. Emigrant Sav. Bank, 619 F.3d 748, 760 (7th Cir. 2010) (“Although we have held that the court in a bench trial need not make reliability determinations before evidence is presented, the determinations must still be made at some point. However, the usual concerns of the rule—
keeping unreliable expert testimony from the jury—are not present in such a setting, and our review must take this factor into consideration. Nevertheless, the ‘court must provide more than just conclusory statements of admissibility or inadmissibility to show that it adequately performed its gatekeeping function.’”) (citations omitted); Attorney Gen. of Okla. v. Tyson Foods, Inc., 565 F.3d 769, 779 (10th Cir. 2009); Seaboard Lumber Co. v. United States, 308 F.3d 1283, 1302 (Fed. Cir. 2002).